To reproduce:

Sub New()
    InitializeComponent()

    ThemeResolutionService.ApplicationThemeName = "Breeze"

    Dim dt As New DataTable
    dt.Columns.Add("Id", GetType(Integer))
    dt.Columns.Add("ParentId", GetType(Integer))
    dt.Columns.Add("Name", GetType(String))

    For index = 1 To 5
        dt.Rows.Add(index, 0, "Parent" & index)
    Next
    Dim rand As New Random
    For index = 6 To 25
        dt.Rows.Add(index, rand.Next(1, 6), "Parent" & index)
    Next
    Me.RadGridView1.Relations.AddSelfReference(Me.RadGridView1.MasterTemplate, "Id", "ParentId")
    Me.RadGridView1.DataSource = dt
    Me.RadGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill

    Me.RadGridView1.AutoSizeRows = True
End Sub

To reproduce:
private void radButton1_Click(object sender, EventArgs e)
{
    radGridView1.Rows[0].Cells[0].Value = false;
}

private void Form1_Load(object sender, EventArgs e)
{
    radGridView1.AllowSearchRow = true;
    radGridView1.TableElement.SearchHighlightColor = Color.Orange;
    radGridView1.AutoExpandGroups = true;

    DataTable dt = new DataTable();

    dt.Columns.Add("test", typeof(bool));

    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);
    dt.Rows.Add(true);

    radGridView1.DataSource = dt;

    ((Telerik.WinControls.UI.GridViewCheckBoxColumn) radGridView1.Columns[0]).EnableHeaderCheckBox = true;
    ((Telerik.WinControls.UI.GridViewCheckBoxColumn) radGridView1.Columns[0]).Width = radGridView1.Width - 50;

    radGridView1.TableElement.Update(Telerik.WinControls.UI.GridUINotifyAction.Reset); //force header checkbox to check

    radGridView1.TableElement.ScrollTo(15, 0);
}

Workaround:
private void radButton1_Click(object sender, EventArgs e)
{
    radGridView1.Rows[0].Cells[0].Value = false;
    radGridView1.TableElement.Update(Telerik.WinControls.UI.GridUINotifyAction.Reset); //force header checkbox to check
}

To reproduce:

private void Form1_Load(object sender, EventArgs e) 
{ 
    this.productsTableAdapter.Fill(this.nwindDataSet.Products);
    this.radGridView1.EnableFiltering = true;
    this.radGridView1.ShowHeaderCellButtons = true;
    this.radGridView1.ShowFilteringRow = false;

    this.radGridView1.Columns["UnitPrice"].FormatString = "{0:$#,###0.00;-$#,###0.00;$0.00}";
}

Workaround:  in order to format the cells, use the CellFormatting event. As to the filter popup, use the following approach:
 this.radGridView1.FilterPopupInitialized += radGridView1_FilterPopupInitialized;

private void radGridView1_FilterPopupInitialized(object sender, Telerik.WinControls.UI.FilterPopupInitializedEventArgs e)
{
    RadListFilterPopup popup = e.FilterPopup as RadListFilterPopup;
    if (popup != null)
    {
        popup.MenuTreeElement.TreeView.NodeFormatting -= TreeView_NodeFormatting;
        popup.MenuTreeElement.TreeView.NodeFormatting += TreeView_NodeFormatting;
    }
}

private void TreeView_NodeFormatting(object sender, TreeNodeFormattingEventArgs e)
{
    decimal price;
    if (decimal.TryParse(e.Node.Text, out price))
    {
        e.NodeElement.ContentElement.Text = string.Format("{0:$#,###0.00;-$#,###0.00;$0.00}", price);
    }
}

Please refer to the attached project.

Workakround: call the BeginEdit method in the RadGridView.Click event.

To reproduce: setup the hierarchy at design time: http://docs.telerik.com/devtools/winforms/gridview/hierarchical-grid/tutorial-binding-to-hierarchical-data

Please refer to the attached gif file illustrating the exact steps.

NOTE: when the "Object does not match target type" error message is displayed, some of the properties are missing, e.g. MaxLength.

Workaround: modify the columns' properties at run time.

To reproduce: follow the steps illustrated in the attached gif file.

To reproduce:

private void Form1_Load(object sender, EventArgs e)
{
    this.productsTableAdapter.Fill(this.nwindDataSet.Products);
    this.radGridView1.BestFitColumns(BestFitColumnMode.AllCells);
}

private void radGridView1_ViewCellFormatting(object sender, Telerik.WinControls.UI.CellFormattingEventArgs e)
{
    if (e.CellElement is GridGroupContentCellElement)
    {
        e.CellElement.TextWrap = true;
    }
    else
    {
        e.CellElement.ResetValue(LightVisualElement.TextWrapProperty, ValueResetFlags.Local);
    }
}

Workaround: set the AutoSizeColumnsMode property to GridViewAutoSizeColumnsMode.Fill and use the ViewCellFormatting event to wrap the text: 

private void radGridView1_ViewCellFormatting(object sender, Telerik.WinControls.UI.CellFormattingEventArgs e)
{
    if (e.CellElement is GridGroupContentCellElement)
    {
        e.CellElement.TextWrap = true;
    }
    else
    {
        e.CellElement.ResetValue(LightVisualElement.TextWrapProperty, ValueResetFlags.Local);
    }
}

How to reproduce: 

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        this.radGridView1.DataSource = this.GetData();
        this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;
        this.radGridView1.Columns[0].DisableHTMLRendering = false;

        this.radGridView1.PrintCellFormatting += radGridView1_PrintCellFormatting;
    }

    private void radGridView1_PrintCellFormatting(object sender, Telerik.WinControls.UI.PrintCellFormattingEventArgs e)
    {
        e.PrintCell.EnableHtmlTextRendering = true;
    }

    private DataTable GetData()
        {
            DataTable dt = new DataTable();

            dt.Columns.Add("Name", typeof(string));
            dt.Columns.Add("Date", typeof(DateTime));
            dt.Columns.Add("Bool", typeof(bool));
            dt.Columns.Add("Description", typeof(string));
            for (int i = 0; i < 10; i++)
            {
                for (int j = 0; j < 5; j++)
                {
                    dt.Rows.Add(@"<html><b>Name " + j, DateTime.Now.AddDays(i), i % 2 == 0 ? true : false, "Description " + i);
                }
            }

            return dt;
        }

    private void radButton1_Click(object sender, EventArgs e)
    {
        GridPrintStyle style = new GridPrintStyle();
        style.FitWidthMode = PrintFitWidthMode.FitPageWidth;
        style.PrintGrouping = true;
        style.PrintSummaries = false;

        style.PrintHeaderOnEachPage = true;
        style.PrintHiddenColumns = false;
        style.CellPadding = new Padding(100, 0, 0, 0);

        this.radGridView1.PrintStyle = style;
        this.radGridView1.PrintPreview();
    }
}


Workaround: refer to the attached project

To reproduce:

this.radGridView1.EnableFiltering = true;
this.radGridView1.Columns.Add("Test column");
this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;
this.radGridView1.Rows.Add("Test ");

Workaround: use custom filtering: 

this.radGridView1.EnableCustomFiltering = true;
this.radGridView1.CustomFiltering += radGridView1_CustomFiltering;


private void radGridView1_CustomFiltering(object sender, GridViewCustomFilteringEventArgs e)
{
    if (this.radGridView1.FilterDescriptors.Count > 0)
    {
        GridViewCellInfo cell = e.Row.Cells[this.radGridView1.FilterDescriptors[0].PropertyName];
        e.Visible = cell.Value.ToString().StartsWith(this.radGridView1.FilterDescriptors[0].Value.ToString());
    }
}

To reproduce: populate RadGridView with data and use the following code snippet:
Me.RadGridView1.TableElement.TableHeaderHeight = 60
RadGridView1.PrintPreview()

Workaround:

Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
    Me.RadGridView1.TableElement.TableHeaderHeight = 60
    Dim printStyle As GridPrintStyle = New GridPrintStyle(RadGridView1)
    Dim renderer As CustomTableViewDefinitionPrintRenderer = New CustomTableViewDefinitionPrintRenderer(RadGridView1)
    printStyle.PrintRenderer = renderer
    RadGridView1.PrintStyle = printStyle
    RadGridView1.PrintPreview()
End Sub

Public Class CustomTableViewDefinitionPrintRenderer
Inherits TableViewDefinitionPrintRenderer

    Public Sub New(grid As RadGridView)
        MyBase.New(grid)

    End Sub

    Private Function GetRowLayout(row As GridViewRowInfo, fitWidthMode As PrintFitWidthMode, _
                                  hierarchyIndent As Integer, drawArea As Rectangle) As TableViewRowLayout
        Dim hashKey As Integer = row.ViewTemplate.GetHashCode() + row.HierarchyLevel
        Dim fi As FieldInfo = GetType(TableViewDefinitionPrintRenderer).GetField("rowLayouts", BindingFlags.NonPublic Or BindingFlags.Instance)
        Dim rowLayouts As Dictionary(Of Integer, TableViewRowLayout) = fi.GetValue(Me)
        If rowLayouts.ContainsKey(hashKey) Then
            Return rowLayouts(hashKey)
        End If

        Dim table As GridTableElement = TryCast(row.ViewTemplate.ViewDefinition.CreateViewUIElement(row.ViewInfo), GridTableElement)
        table.Initialize(Me.GridView.GridViewElement, row.ViewInfo)
        table.RowHeight = Me.GridView.TableElement.RowHeight
        table.TableHeaderHeight = Me.GridView.TableElement.TableHeaderHeight
        Me.GridView.ElementTree.ApplyThemeToElement(table)

        Dim rowLayout As New TableViewRowLayout()
        rowLayout.Context = GridLayoutContext.Printer
        rowLayout.Initialize(table)

        Dim systemWidth As Integer = 0

        For Each c As GridViewColumn In rowLayout.RenderColumns
            If TypeOf c Is GridViewRowHeaderColumn OrElse TypeOf c Is GridViewIndentColumn Then
                systemWidth += rowLayout.GetColumnWidth(c)
            End If
        Next

        Me.GridView.BeginUpdate()

        Dim mode As GridViewAutoSizeColumnsMode = rowLayout.ViewTemplate.AutoSizeColumnsMode

        If fitWidthMode = PrintFitWidthMode.FitPageWidth Then
            Dim state As ColumnsState = Me.SaveColumnsState(rowLayout.ViewTemplate)
            rowLayout.ViewTemplate.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill
            Dim groupLevel As Integer = If(row.Group IsNot Nothing, row.Group.Level + 1, 0)
            rowLayout.MeasureRow(New SizeF(drawArea.Width + systemWidth - ((row.HierarchyLevel - groupLevel) * hierarchyIndent), drawArea.Height))
            Me.RestoreColumnsState(state)
        Else
            rowLayout.ViewTemplate.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.None
            rowLayout.MeasureRow(New SizeF(Me.GridView.Width, Me.GridView.Height))
        End If

        rowLayout.ViewTemplate.AutoSizeColumnsMode = mode

        Me.GridView.EndUpdate(False)

        rowLayouts.Add(hashKey, rowLayout)

        Return rowLayout
    End Function

    Public Overrides Sub DrawPage(traverser As PrintGridTraverser, drawArea As Rectangle, _
                                  graphics As Graphics, settings As GridPrintSettings, pageNumber As Integer)
        Dim fi As FieldInfo = GetType(TableViewDefinitionPrintRenderer).GetField("currentPage", BindingFlags.Instance Or BindingFlags.NonPublic)
        Dim currentPage As Integer = fi.GetValue(Me)
        Dim skipPage As Boolean = currentPage <> pageNumber
        Dim drawAreaHeight As Integer = drawArea.Height
        Dim currentX As Integer = drawArea.X
        Dim currentY As Integer = drawArea.Y

        Dim rowLayout As TableViewRowLayout = Me.GetRowLayout(Me.GridView.MasterView.TableHeaderRow, _
                                                              settings.FitWidthMode, settings.HierarchyIndent, drawArea)
        rowLayout.IgnoreColumnVisibility = settings.PrintHiddenColumns

        Dim systemWidth As Integer = 0

        For Each c As GridViewColumn In rowLayout.RenderColumns
            If TypeOf c Is GridViewRowHeaderColumn OrElse TypeOf c Is GridViewIndentColumn Then
                systemWidth += rowLayout.GetColumnWidth(c)
            End If
        Next

        Dim rowWidth As Integer = CInt(rowLayout.DesiredSize.Width) - systemWidth

        If settings.FitWidthMode = PrintFitWidthMode.NoFitCentered Then
            currentX += ((drawArea.Width - rowWidth) / 2)
        End If

        Dim fi2 As FieldInfo = GetType(TableViewDefinitionPrintRenderer).GetField("firstPage", _
                                                                                  BindingFlags.Instance Or BindingFlags.NonPublic)
        Dim firstPage As Integer = fi2.GetValue(Me)
        If ((Me.GridView.ShowColumnHeaders AndAlso (firstPage AndAlso pageNumber = 1)) OrElse settings.PrintHeaderOnEachPage) _
            AndAlso Not settings.PrintHierarchy Then
            Me.PrintRow(Me.GridView.MasterView.TableHeaderRow, rowLayout, settings, currentX, currentY, graphics, _
                        drawArea)
            Dim rowHeight As Integer = Me.GetDataRowHeight(Me.GridView.MasterView.TableHeaderRow, rowLayout) + Me.GridView.TableElement.RowSpacing
            currentY += rowHeight
            drawAreaHeight -= rowHeight
        End If

        fi2.SetValue(Me, False)
        Dim skipPageCurrentY As Integer = currentY
        Dim row As GridViewRowInfo = Nothing

        If Me.PrintPages.Count > 0 AndAlso Not settings.PrintHierarchy Then
            row = traverser.Current
        End If

        Dim firstRow As Boolean = True

        While traverser.MoveNext()
            If Not (TypeOf traverser.Current Is GridViewDataRowInfo OrElse TypeOf traverser.Current Is GridViewGroupRowInfo OrElse _
                    TypeOf traverser.Current Is GridViewSummaryRowInfo OrElse (TypeOf traverser.Current Is GridViewTableHeaderRowInfo _
                                                                               AndAlso settings.PrintHierarchy)) Then
                Continue While
            End If

            Dim hierarchyRow As GridViewHierarchyRowInfo = TryCast(traverser.Current, GridViewHierarchyRowInfo)

            If hierarchyRow IsNot Nothing AndAlso hierarchyRow.Views.Count > 0 Then
                Select Case settings.ChildViewPrintMode
                    Case ChildViewPrintMode.PrintFirstView
                        hierarchyRow.ActiveView = hierarchyRow.Views(0)
                        Exit Select
                    Case ChildViewPrintMode.PrintCurrentlyActiveView
                        'Do nothing the view is already selected
                        Exit Select
                    Case ChildViewPrintMode.SelectViewToPrint
                        Dim e As New ChildViewPrintingEventArgs(hierarchyRow.Views.IndexOf(hierarchyRow.ActiveView), hierarchyRow)
                        Me.OnChildViewPrinting(e)
                        hierarchyRow.ActiveView = hierarchyRow.Views(e.ActiveViewIndex)
                        Exit Select
                End Select
            End If

            rowLayout = Me.GetRowLayout(traverser.Current, settings.FitWidthMode, settings.HierarchyIndent, drawArea)

            Dim rowHeight As Integer = 0

            If TypeOf traverser.Current Is GridViewGroupRowInfo Then
                rowHeight = Me.GetRowSize(traverser.Current, rowLayout).Height
            Else
                rowHeight = Me.GetDataRowHeight(traverser.Current, rowLayout)
            End If

            If (currentY + rowHeight >= drawArea.Bottom OrElse skipPageCurrentY + rowHeight >= drawArea.Bottom) AndAlso Not firstRow Then
                traverser.MovePrevious()
                skipPageCurrentY = currentY
                skipPage = currentPage <> pageNumber
                fi.SetValue(Me, currentPage + 1)

                If skipPage Then
                    Continue While
                Else
                    Exit While
                End If
            End If

            If TypeOf traverser.Current Is GridViewGroupRowInfo Then
                If settings.PrintGrouping Then
                    If currentPage = pageNumber Then
                        Me.PrintRowWideCell(traverser.Current, rowLayout, settings, currentX, currentY, graphics)
                        currentY += rowHeight + Me.GridView.TableElement.RowSpacing
                    Else
                        skipPageCurrentY += rowHeight + Me.GridView.TableElement.RowSpacing
                    End If
                End If
            Else
                If TypeOf traverser.Current Is GridViewSummaryRowInfo AndAlso Not settings.PrintSummaries Then
                    Continue While
                End If

                If currentPage = pageNumber Then
                    Me.PrintRow(traverser.Current, rowLayout, settings, currentX, currentY, graphics, _
                                drawArea)
                    currentY += rowHeight + Me.GridView.TableElement.RowSpacing
                Else
                    skipPageCurrentY += rowHeight + Me.GridView.TableElement.RowSpacing
                End If
            End If

            If drawAreaHeight < rowHeight AndAlso firstRow Then
                fi.SetValue(Me, currentPage + 1)

                Exit While
            End If

            firstRow = False
        End While

        If Me.PrintPages.Count > 0 AndAlso Not settings.PrintHierarchy Then
            If currentY + Me.GetDataRowHeight(traverser.Current, rowLayout) < drawArea.Bottom OrElse _
                skipPageCurrentY + Me.GetDataRowHeight(traverser.Current, rowLayout) < drawArea.Bottom Then
                fi.SetValue(Me, currentPage + 1)
            End If

            Me.CurrentPrintPage += 1
            Me.CurrentPrintPage = Me.CurrentPrintPage Mod Me.PrintPages.Count

            If Me.CurrentPrintPage > 0 Then
                If row Is Nothing Then
                    traverser.Reset()
                Else
                    traverser.GoToRow(row)
                End If
            End If
        End If
    End Sub
End Class

To reproduce:
Open the attached project, select two rows and delete them.

Workaround:
private void RadGridView1_RowValidating(object sender, Telerik.WinControls.UI.RowValidatingEventArgs e)
{
    if (e.RowIndex != -1)
    {
       
    }
}

To reproduce:
- Bind the grid and reset its data source in the CellValueChanged event handler.
- Start the application, click in a cell, delete the contents and right click a header cell.
- Exception is thrown.

Workaround:

class MyGridHeaderCellElement : GridHeaderCellElement
{
    public MyGridHeaderCellElement(GridViewColumn col, GridRowElement row) : base(col, row)
    { }
    protected override Type ThemeEffectiveType
    {
        get
        {
            return typeof(GridHeaderCellElement);
        }
    }
    protected override void ShowContextMenu()
    {
        if (this.ViewTemplate != null)
        {
            base.ShowContextMenu();
        }
      
    }
}
private void RadGridView1_CreateCell(object sender, GridViewCreateCellEventArgs e)
{
    if (e.CellType == typeof(GridHeaderCellElement))
    {
        e.CellType = typeof(MyGridHeaderCellElement);
    }
}

To reproduce:
- Bind the grid to progress binding source at design time. 
- Locate GroupDescriptors in Properties and click the ellipsis button to open the GroupDescriptor Collection Editor.
- Click Add and select the new item.
- Select the GroupNames collection to open the SortDescriptor Collection Editor.
- Click Add.
- An exception is thrown and the UI freezes.

Workaround:
Add descriptors at runime.

To reproduce: please refer to the attached sample project.

1. Edit the CommonInt property for the first child row.
2. Edit the CommonInt property for the second child row.

Workaround: Add the grid programmatically at run time.

Second Workaround: 

this.radGridView1.CellValueChanged+=radGridView1_CellValueChanged;

private void radGridView1_CellValueChanged(object sender, GridViewCellEventArgs e)
        {
            e.Column.OwnerTemplate.Refresh(e.Column);
        }

To reproduce:
- Add DateTime column and set the RowHeight to 20.
- Set the theme to Windows7.
- The text is not visible when the editor is shown.

Workaround:
private void RadGridView2_CellEditorInitialized(object sender, GridViewCellEventArgs e)
{
    RadDateTimeEditor editor = e.ActiveEditor as RadDateTimeEditor;
    if (editor != null)
    {
        var element = editor.EditorElement as RadDateTimeEditorElement;
        element.Font = new Font("Segoe UI", 8, FontStyle.Regular);
        element.Children[1].Visibility = ElementVisibility.Collapsed;
        element.TextBoxElement.ShowBorder = false;        
        element.TextBoxElement.TextBoxItem.HostedControl.MinimumSize = new Size(0, 12);
    }
}

How to reproduce:
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        this.radGridView1.DataSource = this.GetSampleData();
        this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
        this.radGridView1.EnableFiltering = true;
        this.radGridView1.ShowFilteringRow = false;
        this.radGridView1.ShowHeaderCellButtons = true;
    }

    private DataTable GetSampleData()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("Id", typeof(double));
        dt.Columns.Add("Name", typeof(string));
        dt.Columns.Add("IsValid", typeof(bool));
        dt.Columns.Add("Date", typeof(DateTime));

        for (int i = 0; i < 115; i++)
        {
            dt.Rows.Add(((double)i * 5 / 7) * 3, "Name " + i, i % 2 == 0, DateTime.Now.AddDays(i));
        }

        return dt;
    }
}

Workaround specify decimal as the type of the column in the DataTable object or clone the DataTAble object and change the type of the column:
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        DataTable dt = this.GetSampleData();
        DataTable dtCloned = dt.Clone();
        dtCloned.Columns[0].DataType = typeof(decimal);
        foreach (DataRow row in dt.Rows)
        {
            dtCloned.ImportRow(row);
        }

        this.radGridView1.DataSource = dtCloned;
        this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
        this.radGridView1.EnableFiltering = true;
        this.radGridView1.ShowFilteringRow = false;
        this.radGridView1.ShowHeaderCellButtons = true;
    }

    private DataTable GetSampleData()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("Id", typeof(double));
        dt.Columns.Add("Name", typeof(string));
        dt.Columns.Add("IsValid", typeof(bool));
        dt.Columns.Add("Date", typeof(DateTime));

        for (int i = 0; i < 115; i++)
        {
            dt.Rows.Add(((double)i * 5 / 7) * 3, "Name " + i, i % 2 == 0, DateTime.Now.AddDays(i));
        }

        return dt;
    }
}

To reproduce:

public Form1()
{
    InitializeComponent();
    List<Item> items = new List<Item>();
    for (int i = 0; i < 10; i++)
    {
        items.Add(new Item(i,"Item" + i,Color.Red));
    }
    this.radGridView1.DataSource = items;
    this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;
    this.radGridView1.CellValidating += radGridView1_CellValidating;
}

private void radGridView1_CellValidating(object sender, Telerik.WinControls.UI.CellValidatingEventArgs e)
{
    if (e.ActiveEditor != null && e.ActiveEditor is GridColorPickerEditor)
    {
        Color c = (Color)e.Value;
        if (c == Color.Red)
        {
            e.Cancel = true;
            Console.WriteLine("Red is not allowed!");
        }
    }
}

public class Item
{
    public int Id { get; set; }

    public string Name { get; set; }

    public Color Color { get; set; }

    public Item(int id, string name, Color color)
    {
        this.Id = id;
        this.Name = name;
        this.Color = color;
    }
}

Steps:
1. Activate the editor for the Color cell.
2. Leave the color as it
3. Press the Enter key. The CellValidating event is fired twice.

Note: it seems that when the color text is selected, the event is fired twice.

Please refer to the attached sample project and gif files. The user is not allowed to drop in the first half of the row element. However, the drop operation is allowed in the second half. Once the RadDragOverEventArgs.CanDrop property is set to false, the before/after row hint is disposed and it is not shown for this row anymore.

Workaround: 

public class CustomRadGridViewDragDropService : RadGridViewDragDropService
{
    public CustomRadGridViewDragDropService(RadGridViewElement gridViewElement) : base(gridViewElement)
    {
    }

    public override string Name
    {
        get
        {
            return typeof(RadGridViewDragDropService).Name;
        }
    }

    protected override void OnPreviewDragOver(RadDragOverEventArgs e)
    {
        base.OnPreviewDragOver(e);
        SetDragDropBehavior();
        Point p = this.GridViewElement.ElementTree.Control.PointToClient(Cursor.Position);
        UpdateDragHintLocation(p);
    }
}


this.radGridView1.GridViewElement.RegisterService(new CustomRadGridViewDragDropService(this.radGridView1.GridViewElement));  

To reproduce:

 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load 
     Me.CategoriesTableAdapter.Fill(Me.NwindDataSet.Categories)

     Me.RadGridView1.DataSource = Me.CategoriesBindingSource

     Dim viewDef As New ColumnGroupsViewDefinition
     Dim group1 = New GridViewColumnGroup()
     Dim row1 = New GridViewColumnGroupRow
     group1.Rows.Add(row1)
     row1.ColumnNames.Add("CategoryID")
     row1.ColumnNames.Add("CategoryName")
     viewDef.ColumnGroups.Add(group1)

     Dim group2 = New GridViewColumnGroup()
     Dim row2 = New GridViewColumnGroupRow
     group2.Rows.Add(row2)
     row2.ColumnNames.Add("Description")
     row2.ColumnNames.Add("Picture")
     viewDef.ColumnGroups.Add(group2)

     Me.RadGridView1.ViewDefinition = viewDef
 End Sub

 Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
     Console.WriteLine("BEFORE >>")
     For Each col As GridViewColumn In Me.RadGridView1.Columns
         Console.WriteLine(col.Name & " >> " & col.Width )
     Next

     Dim style As New GridPrintStyle()
     style.FitWidthMode = PrintFitWidthMode.FitPageWidth
     Me.RadGridView1.PrintStyle = style
     Me.RadGridView1.PrintPreview()

     Console.WriteLine("AFTER >>")
     For Each col As GridViewColumn In Me.RadGridView1.Columns
         Console.WriteLine(col.Name & " >> " & col.Width)
     Next
 End Sub

IMPORTANT: If you resize one of the columns at run time before calling the PrintPreview method, the columns' width is restored. In addition, if you call the PrintPreview method without resizing the columns before that, close the dialog and hide one of the columns by using the default context menu, the columns' width for the visible columns is enlarged.

Workaround: you can get the columns width by using the ColumnGroupRowLayout:

Dim rowLayout As ColumnGroupRowLayout = TryCast(Me.RadGridView1.TableElement.ViewElement.RowLayout, ColumnGroupRowLayout)
 
For Each col As GridViewColumn In Me.RadGridView1.Columns
    Dim info As ColumnGroupsCellArrangeInfo = rowLayout.GetColumnData(col)
    Debug.WriteLine(col.Name & " >> " & info.Bounds.Width)
Next

To reproduce:

 public RadForm1()
 {
     InitializeComponent();
     
     DataTable master = new DataTable();
     master.Columns.Add("ID", typeof(int));
     master.Columns.Add("test", typeof(string));
     
     for (int i = 0; i < 500; i++)
     {
         master.Rows.Add(i, "Row " + i);
     }

     radGridView1.DataSource = master;

     radLabel1.Text = "RadGridView: AutoSizeRows = " + ((radGridView1.AutoSizeRows) ? "True" : "False");
 }

 private void radButton1_Click(object sender, EventArgs e)
 {
     radGridView1.TableElement.ScrollToRow(radGridView1.MasterTemplate.Rows[200]);
 }

 private void radButton2_Click(object sender, EventArgs e)
 {
     radGridView1.AutoSizeRows = !radGridView1.AutoSizeRows;

     radLabel1.Text = "RadGridView: AutoSizeRows = " + ((radGridView1.AutoSizeRows) ? "True" : "False");
 }


Workaround:

this.radGridView1.ViewDefinition = new CustomTableViewDefinition();


        public class CustomTableViewDefinition : TableViewDefinition
        {
            public override IRowView CreateViewUIElement(GridViewInfo viewInfo)
            {
                return new CustomGridTableElement();
            }
        }

        public class CustomGridTableElement : GridTableElement
        {
              protected override Type ThemeEffectiveType     
                 { 
                    get    
                              { 
                                     return typeof(GridTableElement);     
                               }
                   }
            public override void ScrollToRow(GridViewRowInfo rowInfo)
            {
                if (rowInfo == null || rowInfo.IsPinned || !rowInfo.IsVisible || rowInfo is GridViewDetailsRowInfo)
                {
                    return;
                }

                this.ViewElement.InvalidateMeasure();
                this.ViewElement.UpdateLayout();

                if (GridViewElement.AutoSizeRows || (ViewTemplate.Templates.Count > 0 && rowInfo.ViewTemplate.Parent != null))
                {
                    ScrollToRowCore(rowInfo, false);

                    return;
                }

                this.RowScroller.ScrollToItem(rowInfo, false);
                this.UpdateLayout();
            }

            private void ScrollToRowCore(GridViewRowInfo rowInfo, bool ensureVisible)
            {
                if (!this.GridViewElement.UseScrollbarsInHierarchy && this.ViewInfo.ParentRow != null)
                {
                    if (ensureVisible)
                    {
                        this.GridViewElement.TableElement.EnsureRowVisible(rowInfo);
                    }
                    else
                    {
                        this.GridViewElement.TableElement.ScrollToRow(rowInfo);
                    }
                    return;
                }

                if (!this.IsInValidState(true) || this.VScrollBar.LargeChange == 0)
                {
                    return;
                }

                RadControl control = this.ElementTree.Control as RadControl;
                if (control != null)
                {
                    control.SuspendUpdate();
                }

                int oldValue = this.VScrollBar.Value;
                GridRowElement rowElement = GetChildRowElement(rowInfo);
                
                if (rowElement == null && this.PageViewMode == PageViewMode.ExplorerBar)
                {
                    if (control != null)
                    {
                        control.ResumeUpdate();
                    }

                    return;
                }

                while (this.VScrollBar.Value < this.VScrollBar.Maximum)
                {
                    if (rowElement == null)
                    {
                        rowElement = GetChildRowElement(rowInfo);
                    }
                    if (rowElement != null)
                    {
                        ScrollToPartiallyVisibleRow(rowElement, ensureVisible);
                        break;
                    }
                    else
                    {
                        bool scrollRangeChanged = SetScrollValue(this.VScrollBar, this.VScrollBar.Value + this.VScrollBar.SmallChange);
                        if (this.VScrollBar.Value >= this.VScrollBar.Maximum - this.VScrollBar.LargeChange + 1 && !scrollRangeChanged)
                        {
                            SetScrollValue(this.VScrollBar, oldValue);
                            break;
                        }
                    }
                }

                if (oldValue == this.VScrollBar.Minimum || rowElement != null)
                {
                    if (control != null)
                    {
                        control.ResumeUpdate();
                    }
                    return;
                }

                SetScrollValue(this.VScrollBar, 0);

                while (this.VScrollBar.Value < oldValue)
                {
                    if (rowElement == null)
                    {
                        rowElement = GetChildRowElement(rowInfo);
                    }
                    if (rowElement != null)
                    {
                        ScrollToPartiallyVisibleRow(rowElement, ensureVisible);
                        break;
                    }
                    else
                    {
                        bool scrollRangeChanged = SetScrollValue(this.VScrollBar, this.VScrollBar.Value + this.VScrollBar.SmallChange);
                        if (this.VScrollBar.Value >= this.VScrollBar.Maximum - this.VScrollBar.LargeChange + 1 && !scrollRangeChanged)
                        {
                            SetScrollValue(this.VScrollBar, oldValue);
                            break;
                        }
                    }
                }

                if (control != null)
                {
                    control.ResumeUpdate();
                }
            }

            private GridRowElement GetChildRowElement(GridViewRowInfo rowInfo)
            {
                if (rowInfo.ViewInfo == this.ViewInfo)
                {
                    return GetRowElement(rowInfo);
                }
                else
                {
                    GridTableElement tableElement = GridViewElement.GetRowView(rowInfo.ViewInfo) as GridTableElement;
                    if (tableElement != null)
                    {
                        return tableElement.GetRowElement(rowInfo);
                    }
                }
                return null;
            }

            private void ScrollToPartiallyVisibleRow(GridRowElement rowElement, bool ensureVisible)
            {
                int delta = 0;

                while ((rowElement.ControlBoundingRectangle.Y < ViewElement.ScrollableRows.ControlBoundingRectangle.Y &&
                        rowElement.ControlBoundingRectangle.Bottom > ViewElement.ScrollableRows.ControlBoundingRectangle.Y) ||
                       (rowElement.ControlBoundingRectangle.Y < ViewElement.ScrollableRows.ControlBoundingRectangle.Bottom &&
                        rowElement.ControlBoundingRectangle.Bottom > ViewElement.ScrollableRows.ControlBoundingRectangle.Bottom))
                {
                    if (rowElement.ControlBoundingRectangle.Y < ViewElement.ScrollableRows.ControlBoundingRectangle.Y &&
                        rowElement.ControlBoundingRectangle.Bottom > ViewElement.ScrollableRows.ControlBoundingRectangle.Y)
                    {
                        delta = ViewElement.ScrollableRows.ControlBoundingRectangle.Y - rowElement.ControlBoundingRectangle.Y;
                        SetScrollValue(this.VScrollBar, this.VScrollBar.Value - delta);

                        return;
                    }

                    if (rowElement.ControlBoundingRectangle.Y < ViewElement.ScrollableRows.ControlBoundingRectangle.Bottom &&
                        rowElement.ControlBoundingRectangle.Bottom > ViewElement.ScrollableRows.ControlBoundingRectangle.Bottom)
                    {
                        delta = rowElement.ControlBoundingRectangle.Top - ViewElement.ScrollableRows.ControlBoundingRectangle.Top;
                        SetScrollValue(this.VScrollBar, this.VScrollBar.Value + delta);

                        return;
                    }

                    if (ensureVisible)
                    {
                        delta = rowElement.ControlBoundingRectangle.Bottom - ViewElement.ScrollableRows.ControlBoundingRectangle.Bottom;

                        if (delta < 0)
                        {
                            break;
                        }
                    }
                    else
                    {
                        delta = rowElement.ControlBoundingRectangle.Y - ViewElement.ScrollableRows.ControlBoundingRectangle.Y;

                        if (delta < 0)
                        {
                            delta = 0;
                        }
                    }

                    bool scrollRangeChanged = SetScrollValue(this.VScrollBar, this.VScrollBar.Value + delta);

                    if (this.VScrollBar.Value >= this.VScrollBar.Maximum - this.VScrollBar.LargeChange + 1 || !scrollRangeChanged)
                    {
                        break;
                    }
                }
            }
            
            private bool SetScrollValue(RadScrollBarElement scrollbar, int newValue)
            {
                int max = this.VScrollBar.Maximum;

                if (newValue > scrollbar.Maximum - scrollbar.LargeChange + 1)
                {
                    newValue = scrollbar.Maximum - scrollbar.LargeChange + 1;
                }

                if (newValue < scrollbar.Minimum)
                {
                    newValue = scrollbar.Minimum;
                }

                scrollbar.Value = newValue;
                this.UpdateLayout();

                return max != this.VScrollBar.Maximum;
            }
        }