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;
            }
        }
  

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 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();
    }
}

Create a DataTable with columns Column1, Column2, Column3, Column4, Column5, and bound to RadGridView. Create a second DataTable with columns Column1, Column2a, Column3, Column4, Column5, and re-bind the RadGridView to this DataTable. Instead of the columns appearing in the same order as they are in the second DataTable, they show up as Column1, Column3, Column4, Column5, Column2a in the RadGridView. 

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");
    }
}

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.

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

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();

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:

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

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:

public Form1()
{
    InitializeComponent();
    this.radGridView1.Columns.Add("Name");
    this.radGridView1.Columns.Add("ID");

    this.radGridView1.RowsChanged += radGridView1_RowsChanged;
}

private void radGridView1_RowsChanged(object sender, GridViewCollectionChangedEventArgs e)
{
    Console.WriteLine(e.Action);
    if (e.Action == Telerik.WinControls.Data.NotifyCollectionChangedAction.Add)
    {
        GridViewRowInfo row = e.NewItems[0] as GridViewRowInfo;
        row.Cells["ID"].Value = this.radGridView1.Rows.Count;
    }
}

private void radButton1_Click(object sender, EventArgs e)
{
    this.radGridView1.Rows.Add("Item" + this.radGridView1.Rows.Count);
}

Note: the first firing of the RowsChanged event used to be with Action=Add.

To reproduce:

public Form1()
{
    InitializeComponent();
    for (int i = 0; i < 10; i++)
    {
        this.radGridView1.Columns.Add("column " + i);
    }

    int charsCount = 5;
    for (int i = 0; i < 20; i++)
    {
        this.radGridView1.Rows.Add(new string('0', charsCount), new string('1', charsCount), 
            new string('2', charsCount), new string('3', charsCount), new string('4', charsCount),
            new string('5', charsCount), new string('6', charsCount), new string('7', charsCount), 
            new string('8', charsCount), new string('9', charsCount));
    }
    HtmlViewDefinition view = new HtmlViewDefinition();
    view.RowTemplate.Rows.Add(new RowDefinition());
    view.RowTemplate.Rows.Add(new RowDefinition());
    view.RowTemplate.Rows.Add(new RowDefinition());
    view.RowTemplate.Rows[0].Cells.Add(new CellDefinition("Column 0", 0, 1, 1));
    view.RowTemplate.Rows[0].Cells.Add(new CellDefinition("Column 1", 0, 1, 3));
    view.RowTemplate.Rows[0].Cells.Add(new CellDefinition("Column 2", 0, 1, 1));
    view.RowTemplate.Rows[0].Cells.Add(new CellDefinition("Column 3", 0, 1, 1));
    view.RowTemplate.Rows[0].Cells.Add(new CellDefinition("Column 7", 0, 1, 1));
    view.RowTemplate.Rows[1].Cells.Add(new CellDefinition("Column 4", 0, 1, 2));
    view.RowTemplate.Rows[1].Cells.Add(new CellDefinition("Column 5", 0, 2, 1));
    view.RowTemplate.Rows[1].Cells.Add(new CellDefinition("Column 8", 0, 1, 1));
    view.RowTemplate.Rows[2].Cells.Add(new CellDefinition("Column 6", 0, 2, 1));
    view.RowTemplate.Rows[2].Cells.Add(new CellDefinition("Column 9", 0, 1, 1));

    this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;

    this.radGridView1.ViewDefinition = view;
}

Workaround:
private void radGridView1_SizeChanged(object sender, EventArgs e)
{
    this.radGridView1.MasterTemplate.Refresh();
}

To reproduce: please refer to the attached sample project and gif file. 

Workaround:

private void radGridView1_CellEditorInitialized(object sender, GridViewCellEventArgs e)
        {
            RadDateTimeEditor editor = e.ActiveEditor as RadDateTimeEditor;
            if (editor != null)
            {
                RadDateTimeEditorElement el = editor.EditorElement as RadDateTimeEditorElement;
                if (el != null)
                {
                    el.TextBoxElement.TextBoxItem.GotFocus -= TextBoxItem_GotFocus; 
                    el.TextBoxElement.TextBoxItem.GotFocus += TextBoxItem_GotFocus; 
                }
            }
        }

        private void TextBoxItem_GotFocus(object sender, EventArgs e)
        {
            RadTextBoxItem tb = sender as RadTextBoxItem;
            if (tb != null)
            {
                tb.SelectionLength = 0;
            }
        }

To reproduce:

Sub New()

    InitializeComponent()

    Dim dt As New DataTable()
    dt.Columns.Add("Price", GetType(System.Double))
    dt.Columns.Add("Name", GetType(System.String))
    dt.Columns.Add("Nr", GetType(System.Double))
    For i As Integer = 0 To 49
        dt.Rows.Add(i, "Data" & i, i)
    Next
    With Me.RadGridView1
        .DataSource = dt
        .Columns("Price").FormatString = "{0:C2}"
        .Columns("Nr").FormatString = "{0:N1}"
        .Columns("Price").ExcelExportType = Export.DisplayFormatType.Currency
        '
        .AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill
    End With
    Me.RadGridView1.Columns("Price").ExcelExportType = Export.DisplayFormatType.Currency

    Me.RadGridView1.Columns("Nr").ExcelExportType = Export.DisplayFormatType.Custom
    Me.RadGridView1.Columns("Nr").ExcelExportFormatString = "{0:N1}"

    Me.RadGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill

End Sub

Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
    Dim spreadStreamExport As New GridViewSpreadStreamExport(Me.RadGridView1)
    spreadStreamExport.ExportVisualSettings = True
    Dim fileName As String = "..\..\" + DateTime.Now.ToLongTimeString().Replace(":", "_").ToString() + ".xlsx"
  
    spreadStreamExport.RunExport(fileName, New SpreadStreamExportRenderer())
    Process.Start(fileName)
End Sub

Workaround:
Me.RadGridView1.Columns("Nr").ExcelExportType = Export.DisplayFormatType.Fixed

AddHandler spreadStreamExport.CellFormatting, AddressOf CellFormatting
Private Sub CellFormatting(sender As Object, e As SpreadStreamCellFormattingEventArgs)
        If e.ExportCell.ColumnIndex = 2 Then
            e.ExportCell.ExportFormat = "0.0"
        End If
    End Sub

Workaround: create a custom RadListFilterPopup
private void radGridView1_FilterPopupRequired(object sender, FilterPopupRequiredEventArgs e)
{
    e.FilterPopup = new MyRadListFilterPopup(e.Column);
}

public class MyRadListFilterPopup : RadListFilterPopup
{
    public MyRadListFilterPopup(GridViewDataColumn dataColumn)
        : base(dataColumn, false)
    { }

    protected override RadListFilterDistinctValuesTable GetDistinctValuesTable()
    {
        if (this.DataColumn.OwnerTemplate.HierarchyLevel == 0)
        {
            return base.GetDistinctValuesTable();    
        }

        GridViewColumnValuesCollection distinctValues = this.GetDistinctValuesWithFilter(this.DataColumn);
        RadListFilterDistinctValuesTable valuesTable = new RadListFilterDistinctValuesTable();
        valuesTable.FormatString = this.DataColumn.FormatString;
        valuesTable.DataConversionInfoProvider = this.DataColumn;

        GridViewComboBoxColumn comboBoxColumn = this.DataColumn as GridViewComboBoxColumn;
        if (comboBoxColumn != null && !String.IsNullOrEmpty(comboBoxColumn.ValueMember))
        {
            foreach (object value in distinctValues)
            {
                if (value != null && value != System.DBNull.Value)
                {
                    object rowValue = value;
                    object lookupValue = ((GridViewComboBoxColumn)this.DataColumn).GetLookupValue(value);

                    if (comboBoxColumn.FilteringMode == GridViewFilteringMode.DisplayMember)
                    {
                        rowValue = lookupValue;
                    }

                    if (lookupValue != null)
                    {
                        valuesTable.Add(lookupValue.ToString(), rowValue);
                    }
                }
            }
        }
        else
        {
            foreach (object value in distinctValues)
            {
                valuesTable.Add(value);
            }
        }

        return valuesTable;
    }

    private GridViewColumnValuesCollection GetDistinctValuesWithFilter(GridViewDataColumn column)
    {
        GridViewColumnValuesCollection distinctValues = new GridViewColumnValuesCollection();
        int count = column.OwnerTemplate.ExcelFilteredColumns.Count;
        if ((count > 0 &&
            column == column.OwnerTemplate.ExcelFilteredColumns[count - 1]) || column.OwnerTemplate.HierarchyLevel > 0)
        {
            if (count == 1 || column.OwnerTemplate.HierarchyLevel > 0)
            {
                int index = column.Index;
                if (index >= 0)
                {
                    IList<GridViewRowInfo> templateRows = column.OwnerTemplate.Rows;
                    if (templateRows.Count == 0 && column.OwnerTemplate.Parent != null && column.OwnerTemplate.HierarchyLevel > 0)
                    {
                        templateRows = new List<GridViewRowInfo>();
                        GridViewInfo templateViewInfo = column.OwnerTemplate.MasterViewInfo;
                        for (int i = 0; i < column.OwnerTemplate.Parent.Rows.Count; i++)
                        {
                            GridViewRowInfo parentRow = column.OwnerTemplate.Parent.Rows[i];
                            ((List<GridViewRowInfo>)templateRows).AddRange(column.OwnerTemplate.HierarchyDataProvider.GetChildRows(parentRow, templateViewInfo));
                        }
                    }
                    
                    foreach (GridViewRowInfo row in templateRows)
                    {
                        object cellValue = row.Cells[index].Value;
                        if (!distinctValues.Contains(cellValue))
                        {
                            distinctValues.Add(cellValue);
                        }
                    }
                    if (distinctValues.Count > 0)
                    {
                        return distinctValues;
                    }
                }
            }
        }

        return distinctValues;
    }
}

To reproduce:

Sub New()
     
    InitializeComponent()

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

    For index = 1 To 5
        dt.Rows.Add(index, "Item" & index, "Description" & index)
    Next
    Me.RadGridView1.DataSource = dt
    Me.RadGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill
    
    AddHandler Me.RadGridView1.UserAddingRow, AddressOf UserAddingRow

End Sub

Private Sub UserAddingRow(sender As Object, e As Telerik.WinControls.UI.GridViewRowCancelEventArgs)
    Me.RadGridView1.MasterView.TableAddNewRow.ErrorText = ""
    If String.IsNullOrEmpty(e.Rows(0).Cells(0).Value) Then
        e.Cancel = True
        Me.RadGridView1.MasterView.TableAddNewRow.ErrorText = "Empty value is not allowed!"
    End If
End Sub

1. Click the new row and enter a value in the last cell. 
2. Click outside the new row, e.g. click on a data row. The UserAddingRow event is canceled and the new row remains current. 
3. Click a data row again without any modification on the new row. The new row is not current anymore. 
4. However, you perform step 1and 2 but instead of clicking a data row, the user clicks a header cell, the new row is not current from the first time. It is necessary to forbid the user to exit the new row until the validation passes or the new row is canceled by pressing Enter.

Workaround:  use the CellValidating/RowValidating event for validating.

Steps to reproduce:

1. Add a CompositeFilterDescriptor programmatically as it is demonstrated in the following help article: http://docs.telerik.com/devtools/winforms/gridview/filtering/setting-filters-programmatically-(composite-descriptors)
2. Save the layout.
3. Load the layout.

Workaround: specify the PropertyName property for the CompositeFilterDescriptor.