How to reproduce: check the attached video as well

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

        this.radGridView1.DataSource = this.GetData();
    }

    private DataTable GetData()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("Id", typeof(int));
        dt.Columns.Add("Name", typeof(string));
        dt.Columns.Add("Date", typeof(DateTime));
        dt.Columns.Add("Bool", typeof(bool));
        for (int i = 0; i < 10; i++)
        {
            dt.Rows.Add(i, "Name " + i, DateTime.Now.AddDays(i), i % 2 == 0);
        }

        return dt;
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        this.radGridView1.TableElement.ScrollToRow(0);
        this.radGridView1.Focus();
    }
}

Workaround: call the method if the row is not selected
private void radButton1_Click(object sender, EventArgs e)
{
    if (!this.radGridView1.Rows[0].IsSelected)
    {
        this.radGridView1.TableElement.ScrollToRow(0);    
    }
    
    this.radGridView1.Focus();
}

To reproduce:

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

    Me.ProductsTableAdapter.Fill(Me.NwindDataSet.Products)
    Me.CategoriesTableAdapter.Fill(Me.NwindDataSet.Categories)
    RadGridView1.AutoGenerateHierarchy = True
    RadGridView1.DataSource = Me.NwindDataSet
    RadGridView1.DataMember = "Categories"
End Sub

Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
    Dim style As New GridPrintStyle()
    style.PrintHierarchy = True
    style.HierarchyIndent = 20
    style.ChildViewPrintMode = ChildViewPrintMode.SelectViewToPrint
    Me.RadGridView1.PrintStyle = style
    Me.RadGridView1.PrintPreview()
End Sub

Please refer to the attached gif file.

Workaround:

Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click

    Me.RadGridView1.PrintSettingsDialogFactory = New CustomGridViewPrintSettingsDialogFactory()

    Dim style As New GridPrintStyle()
    style.PrintHierarchy = True
    style.HierarchyIndent = 20
    style.ChildViewPrintMode = ChildViewPrintMode.SelectViewToPrint
    Me.RadGridView1.PrintStyle = style
    Me.RadGridView1.PrintPreview()
End Sub

Public Class CustomGridViewPrintSettingsDialog
Inherits GridViewPrintSettingsDialog 

    Sub New(document As RadPrintDocument)
        MyBase.New(document)
    End Sub
     
    Protected Overrides Sub LoadSettings()
        MyBase.LoadSettings()

        Dim gridView As RadGridView = TryCast(Me.PrintDocument.AssociatedObject, RadGridView)
        Me.printStyleSettingControl.PrintStyle.PrintHierarchy =gridView.PrintStyle.PrintHierarchy 
    End Sub
End Class

Public Class CustomGridViewPrintSettingsDialogFactory
    Implements IPrintSettingsDialogFactory

    Public Function CreateDialog(document As RadPrintDocument) As Form Implements IPrintSettingsDialogFactory.CreateDialog
        Return New CustomGridViewPrintSettingsDialog(document)
    End Function
End Class

Note: if you change the image in Windows8 theme for example, the image is successfully applied.

Workaround: set the CurrentRowHeaderImage property at run time.

To reproduce
- Set the AutoSize and AutoSizeRows properties to true.
- Start editing a cell.
- Exception occurs.

Workaround:
class MyGrid : RadGridView
{
    protected override void OnResize(EventArgs e)
    {
        //base.OnResize(e);
    }
}

To reproduce:

DataTable dt = new DataTable();

public Form1()
{
    InitializeComponent();
 
    for (int i = 0; i < 5; i++)
    {
        dt.Columns.Add("Col" + i);
    }
     
    for (int i = 0; i < 5; i++)
    {
        DataRow row = dt.NewRow();
        dt.Rows.Add(row);
        foreach (DataColumn col in dt.Columns)
        {
            row[col.ColumnName] = randomWord(2, 14);
        }
    }
}

static Random r = new Random();
static string chars = "AEIOUBCDFGHJKLMNPQRSTVWXYZ";

static string randomWord(int minlen, int maxlen)
{
    double d1 = minlen + r.NextDouble() * (maxlen - minlen); 
    
    int len = (int)d1;
    
    char[] word = new char[len];
    for (int i = 0; i < len; ++i)
    {
        int index = ((int)Math.Round(25 * r.NextDouble() + 0.4999999999));
        word[i] = chars[index];
    }
    return new string(word);
}

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

    public string Name { get; set; }

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

private void radButton1_Click(object sender, EventArgs e)
{
    this.radGridView1.Columns.Clear();
    foreach (DataColumn col in dt.Columns)
    {
        this.radGridView1.Columns.Add(col.ColumnName);
        this.radGridView1.Columns.Last().FieldName = col.ColumnName;
    }
     this.radGridView1.BestFitColumns(BestFitColumnMode.AllCells); 
}

private void Form1_Load(object sender, EventArgs e)
{
    this.radGridView1.AutoGenerateColumns = false;
    this.radGridView1.DataSource = dt; 

    foreach (DataColumn col in dt.Columns)
    {
        this.radGridView1.Columns.Add(col.ColumnName); 
        this.radGridView1.Columns.Last().FieldName = col.ColumnName;
    }
     this.radGridView1.BestFitColumns(BestFitColumnMode.AllCells); 
}

Workaround: clear the GroupDescriptors  collection as well and add the GroupDescriptor programmatically: http://docs.telerik.com/devtools/winforms/gridview/grouping/setting-groups-programmatically

Please refer to the attached screenshot.

To reproduce:

public Form1()
{
    InitializeComponent(); 

    DataTable dt = new DataTable();
    dt.Columns.Add("Id", typeof(int));
    dt.Columns.Add("Name", typeof(string));

    for (int i = 0; i < 5; i++)
    {
        dt.Rows.Add(i, "Item" + i);
    }

    Random rand = new Random();
    DataTable dt2 = new DataTable();
    dt2.Columns.Add("Id", typeof(int));
    dt2.Columns.Add("Name2", typeof(string));
    dt2.Columns.Add("ParentId", typeof(int));
    for (int i = 0; i < 20; i++)
    {
        dt2.Rows.Add(i, "Child Item" + i, rand.Next(0, 5));
    }

    radGridView1.DataSource = dt;
    radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
    GridViewTemplate template = new GridViewTemplate();
    template.DataSource = dt2;
    template.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
    radGridView1.MasterTemplate.Templates.Add(template);
    template.Columns["ParentId"].IsVisible = false;

    GridViewRelation relation = new GridViewRelation(radGridView1.MasterTemplate);
    relation.ChildTemplate = template;
    relation.RelationName = "MasterDetail";
    relation.ParentColumnNames.Add("Id");
    relation.ChildColumnNames.Add("ParentId");
    radGridView1.Relations.Add(relation);

    this.radGridView1.EnableFiltering = true;
    this.radGridView1.ShowFilteringRow = false;
    this.radGridView1.ShowHeaderCellButtons = true;
}

Workaround: change the Name property of the column in order to avoid duplicated columns: 

template.Columns["Name"].Name = "Name2";

To reproduce:
- Add a grid to a form and set the EnableHotTracking property to false in the properties window.
- When the application is started the property is reset.

Workaround:
Set the property at runtime.

To reproduce:

private void Form1_Load(object sender, EventArgs e)
{
    this.order_DetailsTableAdapter.Fill(this.nwindDataSet.Order_Details);

    this.radGridView1.DataSource = this.orderDetailsBindingSource;
    this.radGridView1.EnablePaging = true;
    this.radGridView1.AutoSizeRows = true;
}

private void radButton1_Click(object sender, EventArgs e)
{
    this.radGridView1.PrintStyle.PrintAllPages = true;
    this.radGridView1.PrintPreview();
} 

Workaround:  refresh the MasterTemplate after the PrintPreview dialog is closed: 

this.radGridView1.PrintPreview();

this.radGridView1.MasterTemplate.Refresh();

Workaround: change the name of the column
this.radGridView1.Columns["Table:Name"].Name = "Table|Name";

When you export ht grid content to HTML, the exported table contains an 'width' attribute set to 0. It is not possible to change this attribute. This prevents the HTML to be loaded correctly in RadRichTextEditor later.

Please refer to the attached sample project. Activate the editor for the "Notes" column of the first row, don't perform any changes and click another row. You will notice that the  DataRow.RowState is Modified although no change is performed. If you perform the same actions with a MS DataGridView, the RowState is not Modified.

Note: the GridViewRowInfo.IsModified property in the CellEndEdit is also set to true without modifying the cell's value. 

Workaround: handle the CellBeginEdit and CellEndEdit events and compare the values before and after the edit operation:

object initialValue = null;

private void radGridView1_CellBeginEdit(object sender, GridViewCellCancelEventArgs e)
{
    initialValue = e.Row.Cells[e.ColumnIndex].Value;
}

private void radGridView1_CellEndEdit(object sender, GridViewCellEventArgs e)
{
    if (initialValue != e.Value)
    {
        Console.WriteLine("modified");
    }
    else
    {
        Console.WriteLine("NOT modified");
    }
}

To reproduce:

public Form1()
{
    InitializeComponent();

    GridViewComboBoxColumn comboCol = new GridViewComboBoxColumn();         
    comboCol.DataSource = InitComboActive();
    comboCol.ValueMember = "ActiveCode";
    comboCol.DisplayMember = "ActiveDsc";
    comboCol.FieldName = "ActiveCode";

    this.radGridView1.Columns.Add(comboCol);

    this.radGridView1.AutoGenerateColumns = false;
    BindRadGrid();
    this.radGridView1.CellValueChanged += radGridView1_CellValueChanged;
}

private void radGridView1_CellValueChanged(object sender, GridViewCellEventArgs e)
{
    BindRadGrid();
}

private void BindRadGrid()
{
    this.radGridView1.DataSource = null;
    this.radGridView1.DataSource = InitComboData();
}

private DataTable InitComboActive()
{
    DataTable dt = new DataTable("DtActive");
    dt.Columns.Add("ActiveCode");
    dt.Columns.Add("ActiveDsc");

    dt.Rows.Add("0", "InActive");
    dt.Rows.Add("1", "Active");

    return dt;
}

private DataTable InitComboData()
{
    DataTable dt = new DataTable("DtData");
    dt.Columns.Add("Host");
    dt.Columns.Add("ActiveCode");
    dt.Columns.Add("ActiveDsc");
    
    dt.Rows.Add("Host A", "0", "InActive");
    dt.Rows.Add("Host B", "1", "Active");

    return dt;
}

Workaround: use the RadGridView.CellEndEdit instead for rebinding. 
Workaround 2: use the CellValidated event:
private void radGridView1_CellValidated(object sender, CellValidatedEventArgs e)
{
    if (e.Row is GridViewDataRowInfo)
    {
        BindRadGrid();
    }
}

To reproduce:

public RadForm1()
{
    InitializeComponent();
    DataTable dt = new DataTable();
    for (int i = 0; i < 10; i++)
    {
        dt.Columns.Add("Col" + i);
    }

    for (int i = 0; i < 50; i++)
    {
        DataRow dr = dt.NewRow();
        foreach (DataColumn col in dt.Columns)
        {
            dr[col.ColumnName] = "Data." + i + "." + dt.Columns.IndexOf(col);
        }
        dt.Rows.Add(dr);
    }

    this.radGridView1.DataSource = dt;
    this.radGridView1.MasterTemplate.EnablePaging = true;
    this.radGridView1.MasterTemplate.ShowGroupedColumns = true;
}

public void ExportContactToExcelFile(string strFileName)
{
    GridViewSpreadExport spreadExporter = new GridViewSpreadExport(this.radGridView1);
    SpreadExportRenderer exportRenderer = new SpreadExportRenderer();
       
    spreadExporter.PagingExportOption = PagingExportOption.AllPages;
    spreadExporter.ExportVisualSettings = true;
    spreadExporter.SheetName = "Contacts";
    spreadExporter.RunExport(strFileName, exportRenderer);
}

private void radButton1_Click(object sender, EventArgs e)
{
    ExportContactToExcelFile(@"..\..\Export" + DateTime.Now.ToLongTimeString().Replace(":", "_") + ".xlsx");
}
 
Workaround: refresh the MasterTemplate after the export:

private void radButton1_Click(object sender, EventArgs e)
{
    ExportContactToExcelFile(@"..\..\Export" + DateTime.Now.ToLongTimeString().Replace(":", "_") + ".xlsx");
    this.radGridView1.MasterTemplate.Refresh();
}

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;
            }
        }
  

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 void Form1_Load(object sender, EventArgs e)
 { 
     this.productsTableAdapter.Fill(this.nwindDataSet.Products); 
     this.categoriesTableAdapter.Fill(this.nwindDataSet.Categories);

     this.radGridView1.AutoGenerateColumns = false;
     this.radGridView1.DataSource = this.productsBindingSource;
   
     GridViewComboBoxColumn col = new GridViewComboBoxColumn();
     col.DataSource = this.categoriesBindingSource;
     col.MinWidth = 200;
     col.DisplayMember = "Description";
     col.ValueMember = "CategoryID";
     this.radGridView1.Columns.Add(col);

     this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
     this.radGridView1.CellValueChanged += radGridView1_CellValueChanged;
 }

private void radGridView1_CellValueChanged(object sender, GridViewCellEventArgs e)
{
    string value = "{nothing}";

    if (e.Value != null)
    {
        value = Convert.ToString(e.Value);
    }
    RadMessageBox.Show("CellValueChanged. Value >> " + value);
}

Note: if the cell value is not null, the CellValueChanged event is not fired when the selection in drop down is not changed.
Additional scenario: if you use a RadMultiColumnComboBoxElement for this column replaced in the EditorRequired, the issue is reproducible again.

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.

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;
    }
}

Steps to reproduce:
- create a winforms project
- create form (normal windows form, not telerik form)
- create radgridview from toolbox
- right click and open property builder
- select mastertemplate
- set viewdefinition = columngroups view
- add 3-4 columns (textbox, combobox, etc...)
- click ok button at the property builder
- right click on the radgridview and open the property builder
- rename the name and the header text of the first column
- click ok button at the property builder

To reproduce:

public class CustomGridViewCheckBoxColumn : GridViewCheckBoxColumn
        { 
        
        }

CustomGridViewCheckBoxColumn col = new CustomGridViewCheckBoxColumn();
this.radGridView1.Columns.Add(col);
this.radGridView1.EnableFiltering = true;

1. Click the filter button and select "Custom"
2. Close the dialog.

Workaround:

 this.radGridView1.CreateCompositeFilterDialog += radGridView1_CreateCompositeFilterDialog;

private void radGridView1_CreateCompositeFilterDialog(object sender, GridViewCreateCompositeFilterDialogEventArgs e)
{
    e.Dialog = new CustomCompositeFilterForm();
}

public class CustomCompositeFilterForm : CompositeFilterForm
{
    public override void Initialize(GridViewDataColumn dataColumn, FilterDescriptor filterDescriptor, bool useTypedEditors)
    {
        base.Initialize(dataColumn, filterDescriptor, useTypedEditors);
        if (dataColumn is GridViewCheckBoxColumn)
        {
            RadGroupBox groupBox = this.Controls[0] as RadGroupBox;
            groupBox.Controls.Remove(this.RightEditor);
            groupBox.Controls.Remove(this.LeftEditor);
            MethodInfo mi = typeof(CompositeFilterForm).GetMethod("InitializeCheckBoxEditors", BindingFlags.Instance | BindingFlags.NonPublic);
            mi.Invoke(this, null);
        }
    }
}