To reproduce: 
1. Add a RadGridView and bind it to Northwind.Products table.
2. Use the following code:

 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
     Me.ProductsTableAdapter.Fill(Me.NwindDataSet.Products)
     For Each col As GridViewColumn In Me.RadGridView1.Columns
         If Not col.HeaderText = "SupplierID" AndAlso Not col.HeaderText = "ProductID" Then
             col.ReadOnly = True
         End If
     Next
     Me.RadGridView1.AddNewRowPosition = SystemRowPosition.Bottom
 End Sub

 Private Sub RadGridView1_CellValidating(sender As Object, e As CellValidatingEventArgs) Handles RadGridView1.CellValidating
     If e.Value Is Nothing Then
         If MessageBox.Show("Incorrect", "error", MessageBoxButtons.OKCancel) = Windows.Forms.DialogResult.OK Then
             e.Cancel = True
         End If
     End If
 End Sub

3. Run the project and go to the new row ,cell "SupplierID".
4. Clear the value and press Tab key. As a result the message box for error indication is shown twice.

Workaround:
'register the custom row  behavior
Dim gridBehavior As BaseGridBehavior = TryCast(RadGridView1.GridBehavior, BaseGridBehavior)
gridBehavior.UnregisterBehavior(GetType(GridViewNewRowInfo))
gridBehavior.RegisterBehavior(GetType(GridViewNewRowInfo), New MyNewRowBehavior())

Me.RadGridView1.GridViewElement.Navigator = New MyGridNavigator()


Public Class MyNewRowBehavior
Inherits GridNewRowBehavior
    Protected Overrides Function ProcessTabKey(keys As KeyEventArgs) As Boolean
        If Me.GridControl.AddNewRowPosition = SystemRowPosition.Bottom AndAlso _
        Me.GridControl.IsInEditMode AndAlso Me.GridViewElement.Navigator.IsLastColumn(GridViewElement.CurrentColumn) Then
            Me.GridControl.Tag = "SuspendValidation"
        End If
        Return MyBase.ProcessTabKey(keys)
    End Function
End Class

Public Class MyGridNavigator
Inherits BaseGridNavigator
    Public Overrides Function SelectFirstColumn() As Boolean
        If Me.GridViewElement.GridControl.Tag = "SuspendValidation" Then
            Me.GridViewElement.GridControl.Tag = Nothing
            Return False
        End If
        Return MyBase.SelectFirstColumn()
    End Function
End Class

To reproduce: use the attached sample project. Follow the steps illustrated on the attached gif file.

Workaround: keep the vertical scrollbar value and maximum before modifying the child rows and restore them afterwards:

private void gridViewParameter_CellValueChanged(object sender, GridViewCellEventArgs e)
{
   if (e.Column.Name == "Select")
    {
        this.gridViewParameter.CellValueChanged -= gridViewParameter_CellValueChanged;

        GridViewRowInfo selectedRowinfo = e.Row;                  
        if (selectedRowinfo.HasChildRows())
        {
            int scrollValue = this.gridViewParameter.TableElement.VScrollBar.Value;
            int scrollMax = this.gridViewParameter.TableElement.VScrollBar.Maximum;
          
            this._UpdateUiState(selectedRowinfo.ChildRows, Convert.ToBoolean(selectedRowinfo.Cells["Select"].Value));
            
            this.gridViewParameter.TableElement.VScrollBar.Maximum = scrollMax;
            this.gridViewParameter.TableElement.VScrollBar.Value = scrollValue;
        }
        this.gridViewParameter.CellValueChanged += gridViewParameter_CellValueChanged;
    }
}

NOTE: after applying the workaround, there is annoying flickering illustrated on the Flickering.gif file which should be handled if possible.

To reproduce:
- Create a hierarchy  and set the UseScrollbarsInHierarchy property to true.
- Scroll by pressing the thumb in the child template.
-  The CellClick event is fired when the mouse is released.

Workaround:
void radGridView1_CellClick(object sender, GridViewCellEventArgs e)
{
    if (e.Column != null)
    {
        Console.WriteLine("CellClick");
    }
}

The idea is that one can bring into view a certain row.

To reproduce:
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
    Me.ProductsTableAdapter.Fill(Me.NwindDataSet.Products)
    Dim menu As New ContextMenu()
    For index = 1 To 4
        menu.MenuItems.Add("item" & index)
    Next
    Me.ContextMenu = menu
End Sub

Workaround:

Const WM_CONTEXTMENU As Integer = &H7B

Public Class Grid
Inherits RadGridView
    Protected Overrides Sub WndProc(ByRef m As Message)
        If m.Msg = WM_CONTEXTMENU Then
            Return
        End If
        MyBase.WndProc(m)
    End Sub

    Public Overrides Property ThemeClassName As String
        Get
            Return GetType(RadGridView).FullName
        End Get
        Set(value As String)
            MyBase.ThemeClassName = value
        End Set
    End Property
End Class

Workaround
this.radGridView1.Templates["MyEmptyTemplate"]..AddNewRowPosition = SystemRowPosition.Top

Then handle the ViewCellFormatting event and get notifications when the hierarchy tabs are being clicked.
private void radGridView1_ViewCellFormatting(object sender, CellFormattingEventArgs e)
{
	GridDetailViewCellElement detailCell = e.CellElement as GridDetailViewCellElement;
	if (detailCell != null) {
		detailCell.PageViewElement.ItemSelected -= PageViewElement_ItemSelected;
		detailCell.PageViewElement.ItemSelected += PageViewElement_ItemSelected;
	}
}

private void PageViewElement_ItemSelected(object sender, RadPageViewItemSelectedEventArgs e)
{
	if (e.SelectedItem.Text == "MyEmptyTemplate") {
		this.SetsGridViewTemplate.AddNewRowPosition = SystemRowPosition.Bottom;
	}
}

To reproduce:
- Add ColumnGroupsViewDefinition and subscribe to ColumnWidthChanged event.
- Start the application and resize a column.

Workaround:
public class MyColumnGroupRowLayout : ColumnGroupRowLayout
{
    public MyColumnGroupRowLayout(ColumnGroupsViewDefinition view) : base(view)
    {
    }

    public override void ResizeColumn(int delta)
    {
        base.ResizeColumn(delta);
        //This method will be called when a column is resized
    }
}

class MyColumnGroupsViewDefinition : ColumnGroupsViewDefinition
{
    public override IGridRowLayout CreateRowLayout()
    {
        return new MyColumnGroupRowLayout(this);
    }
}

To reproduce:

for (int i = 0; i < 5; i++)
{
    this.radGridView1.Columns.Add("Col" + i);
}

ColumnGroupsViewDefinition columnGroupsView = new ColumnGroupsViewDefinition();
columnGroupsView.ColumnGroups.Add(new GridViewColumnGroup());
columnGroupsView.ColumnGroups.Add(new GridViewColumnGroup());
columnGroupsView.ColumnGroups.Add(new GridViewColumnGroup());
columnGroupsView.ColumnGroups.Add(new GridViewColumnGroup());


columnGroupsView.ColumnGroups[0].Rows.Add(new GridViewColumnGroupRow());
columnGroupsView.ColumnGroups[0].Rows[0].ColumnNames.Add("Col3");


columnGroupsView.ColumnGroups[1].Rows.Add(new GridViewColumnGroupRow());
columnGroupsView.ColumnGroups[1].Rows[0].ColumnNames.Add("Col2");
columnGroupsView.ColumnGroups[2].Rows.Add(new GridViewColumnGroupRow());
columnGroupsView.ColumnGroups[2].Rows.Add(new GridViewColumnGroupRow());
columnGroupsView.ColumnGroups[2].Rows[0].ColumnNames.Add("Col0");
columnGroupsView.ColumnGroups[2].Rows[1].ColumnNames.Add("Col1");

columnGroupsView.ColumnGroups[3].Rows.Add(new GridViewColumnGroupRow());  
columnGroupsView.ColumnGroups[3].Rows[0].ColumnNames.Add("Col4");

this.radGridView1.ViewDefinition = columnGroupsView;

this.radGridView1.Columns["Col2"].Width = 150;
this.radGridView1.Columns["Col0"].Width = 200;


Workaround: either set the columns width before setting the RadGridView.ViewDefinition or call the TableElement.ViewElement.RowLayout.InvalidateRenderColumn after specifying the width.

To reproduce: 

private void Form1_Load(object sender, EventArgs e)
{ 
    this.productsTableAdapter.Fill(this.nwindDataSet.Products);
    this.radGridView1.DataSource = this.productsBindingSource;
    GridViewSummaryItem summaryItem = new GridViewSummaryItem();
    summaryItem.Name = "UnitPrice";
    summaryItem.Aggregate = GridAggregateFunction.Count;
    GridViewSummaryRowItem summaryRowItem = new GridViewSummaryRowItem();
    summaryRowItem.Add(summaryItem);
    this.radGridView1.SummaryRowsTop.Add(summaryRowItem);
    
    GroupDescriptor descriptor1 = new GroupDescriptor();
    descriptor1.GroupNames.Add("CategoryID", ListSortDirection.Ascending);
    this.radGridView1.GroupDescriptors.Add(descriptor1);
    GroupDescriptor descriptor11 = new GroupDescriptor();
    descriptor11.GroupNames.Add("SupplierID", ListSortDirection.Ascending);
    this.radGridView1.GroupDescriptors.Add(descriptor11);
    GroupDescriptor descriptor2 = new GroupDescriptor();
    descriptor2.GroupNames.Add("QuantityPerUnit", ListSortDirection.Ascending);
    descriptor2.GroupNames.Add("UnitsInStock", ListSortDirection.Ascending);
    this.radGridView1.GroupDescriptors.Add(descriptor2);
    GroupDescriptor descriptor3 = new GroupDescriptor();
    descriptor3.GroupNames.Add("UnitsOnOrder", ListSortDirection.Ascending);
    descriptor3.GroupNames.Add("ReorderLevel", ListSortDirection.Descending);
    this.radGridView1.GroupDescriptors.Add(descriptor3);
    GroupDescriptor descriptor4 = new GroupDescriptor();
    descriptor4.GroupNames.Add("Discontinued", ListSortDirection.Ascending);
    this.radGridView1.GroupDescriptors.Add(descriptor4);
}

private void radButton1_Click(object sender, EventArgs e)
{
    GridViewSpreadExport spreadExporter = new GridViewSpreadExport(this.radGridView1);
    SpreadExportRenderer exportRenderer = new SpreadExportRenderer();
    string filePath = @"..\..\exported" + DateTime.Now.ToShortTimeString().Replace(":", "_") + ".xlsx";
    spreadExporter.ExportGroupedColumns = true;
    spreadExporter.ExportChildRowsGrouped = true;
     spreadExporter.HiddenColumnOption = Telerik.WinControls.UI.Export.HiddenOption.DoNotExport;
    spreadExporter.ExportVisualSettings = true;
    spreadExporter.SummariesExportOption = Telerik.WinControls.UI.Export.SummariesOption.ExportAll;
    spreadExporter.RunExport(filePath, exportRenderer);

    Process.Start(filePath);
}


Workaround: set the ExportChildRowsGrouped property to false.

To reproduce: 
1. Add GridView which inherits the RadGridView
2. Populate the grid with some data
3. Add conditional formatting and set RowBackColor and CellBackColor 
4. Subscribe to RowFormatting event and change the font of selected row: 
void radGridView2_RowFormatting(object sender, RowFormattingEventArgs e)
{
    if (e.RowElement.IsSelected)
    {
        e.RowElement.Font = new Font(this.Font.FontFamily, this.Font.Size + 2, FontStyle.Bold);
    }
    else
    {
        e.RowElement.ResetValue(LightVisualElement.FontProperty, ValueResetFlags.Local);
        //e.RowElement.Font = this.Font;
    }
}

5. Select row with conditional formatting. The font of selected row is bold which is correct. Select another row and you will see that the previous row is still bold.

Workaround: 
Subscribe to CellFormatting event instead RowFormatting
void radGridView2_CellFormatting(object sender, CellFormattingEventArgs e)
{
    if (e.Row.IsSelected)
    {
        e.CellElement.Font = new Font(this.Font.FontFamily, this.Font.Size + 2, FontStyle.Bold);
    }
    else
    {
        e.CellElement.ResetValue(LightVisualElement.FontProperty, ValueResetFlags.Local);
    }
}

BindingList<Item> items = new BindingList<Item>();

public Form1()
{
    InitializeComponent();

    for (int i = 0; i < 20; i++)
    {
        items.Add(new Item(i % 4, "Item" + i, "Type" + i % 2));
    }
    this.radGridView1.DataSource = items;
    this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;
}

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

    public string Name { get; set; }

    public string Type { get; set; }

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

private void radButton1_Click(object sender, EventArgs e)
{
    items.Insert(0, new Item(2, "Test", "Type0"));
}

WORKAROUND I:

GridViewSynchronizationService.SuspendEvent(this.radGridView1.MasterTemplate, KnownEvents.CurrentChanged);
Item item = new Item(2, "Test", "Type0");
items.Insert(0, item);
GridViewSynchronizationService.ResumeEvent(this.radGridView1.MasterTemplate, KnownEvents.CurrentChanged);

foreach (GridViewRowInfo row in this.radGridView1.Rows)
{
    if (row.DataBoundItem == item)
    {
        this.radGridView1.CurrentRow = row;

        break;
    }
}



WORKAROUND II:

this.radGridView1.Rows.CollectionChanged += Rows_CollectionChanged;
this.radGridView1.GroupExpanding+=radGridView1_GroupExpanding;

List<GridViewRowInfo> expandedGroups = new List<GridViewRowInfo>();

private void radGridView1_GroupExpanding(object sender, GroupExpandingEventArgs e)
{
    if (!e.IsExpanded && shouldCollapse)
    {
        expandedGroups.Add(e.DataGroup.GroupRow);
    }
}

bool shouldCollapse = false;

private void radButton1_Click(object sender, EventArgs e)
{
    shouldCollapse = true;
    items.Insert(0, new Item(2, "Test", "Type0"));
}

private void Rows_CollectionChanged(object sender, Telerik.WinControls.Data.NotifyCollectionChangedEventArgs e)
{
    if (e.Action == Telerik.WinControls.Data.NotifyCollectionChangedAction.Add)
    {
        this.radGridView1.CurrentRow = e.NewItems[0] as GridViewRowInfo;
        this.radGridView1.CurrentRow.IsSelected = true;
        GridViewRowInfo parent = this.radGridView1.CurrentRow.Parent as GridViewRowInfo;
        if (parent != null)
        {
            parent.IsExpanded = true;
        }

        if (shouldCollapse)
        {
            shouldCollapse = false;
            foreach (GridViewRowInfo r in expandedGroups)
            {
                if (!ContainsParentRow(parent, r))
                {
                    r.IsExpanded = false;
                }
            }
            expandedGroups.Clear();
        }
    }
}

private bool ContainsParentRow(GridViewRowInfo parent, GridViewRowInfo r)
{
    GridViewGroupRowInfo group = r as GridViewGroupRowInfo;
    if (group != null)
    {
        foreach (GridViewRowInfo childRow in group.ChildRows)
        {
            return ContainsParentRow(parent, childRow);
        }
    }

    return parent == r.Parent;
}

To reproduce:
public RadForm1()
{
    InitializeComponent();
    radGridView1.AutoGenerateColumns = false;
  
    GridViewDecimalColumn decimalColumn = new GridViewDecimalColumn();
    decimalColumn.DataType = typeof(int);
    decimalColumn.Name = "DecimalColumn";
    decimalColumn.HeaderText = "DecimalColumn";
    decimalColumn.FieldName = "Dosage";
    decimalColumn.Width = 200;
    radGridView1.MasterTemplate.Columns.Add(decimalColumn);
    
    radGridView1.DataSource = GetTable();
    radGridView1.CellValidating += radGridView1_CellValidating;
    
}

void radGridView1_CellValidating(object sender, CellValidatingEventArgs e)
{
    int value = Convert.ToInt32(e.Value);
}

Workaround:
void radGridView1_CellValidating(object sender, CellValidatingEventArgs e)
{
    int value = Convert.ToInt32(e.Value);
}

To reproduce:

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

    radGridView1.DataSource = nwindDataSet.Categories;
    radGridView1.MasterTemplate.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;

    GridViewTemplate template = new GridViewTemplate();
    template.DataSource = nwindDataSet.Products;
    template.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
    radGridView1.MasterTemplate.Templates.Add(template);

    GridViewRelation relation = new GridViewRelation(radGridView1.MasterTemplate);
    relation.ChildTemplate = template;
    relation.RelationName = "CategoriesProducts";
    relation.ParentColumnNames.Add("CategoryID");
    relation.ChildColumnNames.Add("CategoryID");
    radGridView1.Relations.Add(relation);

     this.radGridView1.CurrentRow = this.radGridView1.MasterTemplate.Templates.First().Rows[this.radGridView1.MasterTemplate.Templates.First().Rows.Count - 1];
}

Workaround:

this.radGridView1.MasterTemplate.ExpandAll();
this.radGridView1.MasterTemplate.CollapseAll();
this.radGridView1.CurrentRow = this.radGridView1.MasterTemplate.Templates.First().Rows[this.radGridView1.MasterTemplate.Templates.First().Rows.Count - 1];


Another scenario: if you try to add a new row to the child template on the RadButton.Click event and call the EnsureVisible(true) method, it will not affect the grid, until you expand/collapse the parent row:

private void radButton1_Click(object sender, EventArgs e)
{
    //add the new row to the child template
    DataRow newRow = this.nwindDataSet.Products.Rows.Add();
    newRow["CategoryID"] = 3;
    newRow["ProductName"] = "NewProduct";

    this.radGridView1.CurrentRow = this.radGridView1.MasterTemplate.Templates.First().Rows[this.radGridView1.MasterTemplate.Templates.First().Rows.Count - 1];
    this.radGridView1.CurrentRow.EnsureVisible(true);
}

Workaround:

private void radButton1_Click(object sender, EventArgs e)
{
    //keep expanded rows
    List<GridViewRowInfo> expandedRows = new List<GridViewRowInfo>();
    foreach (GridViewRowInfo row in this.radGridView1.Rows)
    {
        if (row.IsExpanded)
        {
            expandedRows.Add(row);
        }
    }
    
    //add the new row to the child template
    DataRow newRow = this.nwindDataSet.Products.Rows.Add();
    newRow["CategoryID"] = 3;
    newRow["ProductName"] = "NewProduct";

    //refresh the rows
    this.radGridView1.MasterTemplate.ExpandAll();
    this.radGridView1.MasterTemplate.CollapseAll();

    foreach (GridViewRowInfo rowToExpand in expandedRows)
    {
        rowToExpand.IsExpanded = true;
    }
    this.radGridView1.CurrentRow = null;
    this.radGridView1.CurrentRow = this.radGridView1.MasterTemplate.Templates.First().Rows[this.radGridView1.MasterTemplate.Templates.First().Rows.Count - 1];
    this.radGridView1.CurrentRow.EnsureVisible(true);
}

Please refer to the attached screenshot.

Workaround: either select the RadGridView node in the Property Builder, or use the VS design time or control Smart Tag to set DataSource

To reproduce:

Setup RadGridView as follows:

this.Grid.MasterTemplate.EnablePaging = true;
this.Grid.Columns.Add("");
this.Grid.Columns.Add("");
this.Grid.Columns.Add("");
this.Grid.Columns.Add("");

On a button click add rows:

private void Button_Clic9k(object sender, EventArgs e)
{
    for (int i = 0; i < 120; i++)
    {
        this.Grid.Rows.AddNew();
    }
}

You will see a vertical scrollbar when it is not needed.

Workaround:

Wrap the loop in a Begin/EndUpdate calls:

private void Button_Clic9k(object sender, EventArgs e)
{
    this.Grid.BeginUpdate();
    for (int i = 0; i < 120; i++)
    {
        this.Grid.Rows.AddNew();
    }

    this.Grid.EndUpdate();
}

To reproduce:
- Bind the grid to a DataView. The grid must have combo box column.
- Change the filter of the DataView like this:

Private Sub MasterTemplate_FilterExpressionChanged(sender As Object, e As FilterExpressionChangedEventArgs) Handles RadGridView.FilterExpressionChanged
    _companies.RowFilter = e.FilterExpression
End Sub

- Set a filter to the combo box column and then set reset by selecting no filter in the drop down. 

Workaround:
Public Class MyGridFilterComboBoxCellElement
	Inherits GridFilterComboBoxCellElement

	Public Sub New(ByVal col As GridViewDataColumn, ByVal row As GridRowElement)
		MyBase.New(col, row)
	End Sub
	Protected Overrides Sub SetContentCore(ByVal value As Object)
		If Me.ComboBoxColumnInfo IsNot Nothing Then
			MyBase.SetContentCore(value)
		End If

	End Sub
End Class

Private Sub radGridView1_CreateCell(ByVal sender As Object, ByVal e As GridViewCreateCellEventArgs)
	If e.CellType Is GetType(GridFilterComboBoxCellElement) Then
		e.CellType = GetType(MyGridFilterComboBoxCellElement)
	End If

End Sub

Workaround: before printing set the AutoSizeRows = false, then you can set it again to true

private void radButton1_Click(object sender, EventArgs e)
        {
            if (!this.radGridView1.Columns["ImageColumn"].IsVisible)
            {
                int height = this.radGridView1.TableElement.ViewTemplate.Rows[0].Height;
                this.radGridView1.AutoSizeRows = false;
                this.radGridView1.TableElement.RowHeight = height;
            }

            this.radGridView1.PrintPreview();
            this.radGridView1.AutoSizeRows = true;           
        }

To reproduce:
private void RadForm1_Load(object sender, EventArgs e)
{
	DataTable dt = new DataTable();

	dt.Columns.Add("col1", typeof(bool));
	dt.Columns.Add("col2", typeof(bool));

	dt.Rows.Add(0, 1);
	dt.Rows.Add(0, 1);
	dt.Rows.Add(0, 1);

	RadGridView1.DataSource = dt;

	((Telerik.WinControls.UI.GridViewCheckBoxColumn)RadGridView1.Columns(0)).EnableHeaderCheckBox = true;
	((Telerik.WinControls.UI.GridViewCheckBoxColumn)RadGridView1.Columns(1)).EnableHeaderCheckBox = true;

	RadGridView1.HeaderCellToggleStateChanged += radGridView1_HeaderCellToggleStateChanged;

}

- Start the application and click in the second row in the first column.

Workaraound:
public class MyGridCheckBoxHeaderCellElement : GridCheckBoxHeaderCellElement
{
    public MyGridCheckBoxHeaderCellElement(GridViewDataColumn col, GridRowElement row)
        : base(col, row)
    { }
    protected override void SetCheckBoxState(ToggleState state)
    {
        if (this.ColumnInfo.Name != this.GridViewElement.CurrentCell.ColumnInfo.Name)
        {
            return;
        }
        base.SetCheckBoxState(state);
    }
}

Workaround: use a GridPrintStyle and define a HierarchyIndent = 0
private void PrintGrid()
{
    GridPrintStyle style = new GridPrintStyle();
    style.HierarchyIndent = 0;
    this.radGridView1.PrintStyle = style;
    this.radGridView1.PrintPreview();
}

To reproduce:

public Form1()
{
    InitializeComponent();

    ColumnGroupsViewDefinition columnGroupsView;
     
    columnGroupsView = new ColumnGroupsViewDefinition();
    columnGroupsView.ColumnGroups.Add(new GridViewColumnGroup());
    columnGroupsView.ColumnGroups.Add(new GridViewColumnGroup());
    columnGroupsView.ColumnGroups.Add(new GridViewColumnGroup());
    columnGroupsView.ColumnGroups.Add(new GridViewColumnGroup());

    columnGroupsView.ColumnGroups[0].ShowHeader = false;

    columnGroupsView.ColumnGroups[0].Rows.Add(new GridViewColumnGroupRow());
    columnGroupsView.ColumnGroups[0].Rows[0].ColumnNames.Add("colPINNED_LEFT");

    columnGroupsView.ColumnGroups[1].Rows.Add(new GridViewColumnGroupRow());
    columnGroupsView.ColumnGroups[1].Rows[0].ColumnNames.Add("colDATE");
    columnGroupsView.ColumnGroups[2].Rows.Add(new GridViewColumnGroupRow());
    columnGroupsView.ColumnGroups[2].Rows.Add(new GridViewColumnGroupRow());
    columnGroupsView.ColumnGroups[2].Rows[0].ColumnNames.Add("colTITLE");
    columnGroupsView.ColumnGroups[2].Rows[1].ColumnNames.Add("colTEXT");
   
    columnGroupsView.ColumnGroups[3].Rows.Add(new GridViewColumnGroupRow()); 

    columnGroupsView.ColumnGroups[3].Rows[0].ColumnNames.Add("colPINNED_RIGHT");

    this.radGridView1.ViewDefinition = columnGroupsView;

    this.radGridView1.Columns["colDATE"].Width = 110;
    this.radGridView1.Columns["colTITLE"].Width = this.radGridView1.Width - 181;

    this.radGridView1.TableElement.ViewElement.RowLayout.InvalidateRenderColumns();
    
    columnGroupsView.ColumnGroups[0].PinPosition = PinnedColumnPosition.Left;  
    columnGroupsView.ColumnGroups[3].PinPosition = PinnedColumnPosition.Right; 
    
}

Workaround: do not set the ShowHeader property to false. Use the ViewCellFormatting event to hide to necessary cell borders to simulate cells merging.