To reproduce: use the following code snippet. Navigate to the last page and press the button to clear the rows. You will notice that the current page index remains 10 although no rows are available in the grid

        public RadForm1()
        {
            InitializeComponent();

            this.radVirtualGrid1.RowCount = 1000;
            this.radVirtualGrid1.ColumnCount = 5;
            this.radVirtualGrid1.CellValueNeeded += radVirtualGrid1_CellValueNeeded;

            this.radVirtualGrid1.EnablePaging = true;
        }

        private void radVirtualGrid1_CellValueNeeded(object sender, Telerik.WinControls.UI.VirtualGridCellValueNeededEventArgs e)
        {
            e.Value = "Item" + e.RowIndex + "." + e.ColumnIndex;
        }

        private void radButton1_Click(object sender, EventArgs e)
        {
            this.radVirtualGrid1.RowCount = 0;
            this.radVirtualGrid1.ColumnCount = 5; 
        }

Workaround:  this.radVirtualGrid1.VirtualGridElement.FindDescendant<VirtualGridPagingPanelElement>().PageNumberTextBox.Text = "1";

To reproduce: open the VirtualGrid >> First Look example in QSF and follow the steps:

1) I have a virtual grid which has both vertical and horizontal scroll bars.

2) Scroll to the very bottom of the grid

3) Select the last row

4) Scroll all the way to the right

At this moment the selected row disappears from the view. While scrolling horizontally the vertical scrollbar jumps several rows above although it seems scrolled to the bottom. 

To reproduce: run the sample project and try to resize some of the columns.

RadVirtualGrid has 10 columns and 500 rows. You will notice the laggind while resizing the columns. Actually the number of the visible cells remains the same after the column's resizing. However, the CellValueNeeded event keeps firing.

The attached gif file illustrates how to reproduce the problem with the Demo application. 

Use attached to reproduce (just start it and press enter).

Workaround:

class MyBehavior : VirtualGridInputBehavior
{
    public MyBehavior(RadVirtualGridElement element) : base(element)
    {

    }
    protected override bool HandleEnterKey(KeyEventArgs keys)
    {
        if (this.GridElement.CurrentCell != null)
        {
            return base.HandleEnterKey(keys);
        }
        return false; 
    }
}


radVirtualGrid1.VirtualGridElement.InputBehavior = new MyBehavior(radVirtualGrid1.VirtualGridElement);

To reproduce:
- Enable the paging and add 1000 rows.
- Press Ctrl + End
- An exception is thrown.

Workaround:

radVirtualGrid1.VirtualGridElement.InputBehavior = new MyBehavior(radVirtualGrid1.VirtualGridElement);

class MyBehavior : VirtualGridInputBehavior
{
    public MyBehavior(RadVirtualGridElement element) : base(element)
    {

    }
    protected override bool HandleEndKey(KeyEventArgs keys)
    {
        this.GridElement.PageIndex = this.GridElement.TotalPages - 1;
      
        return true;
        //return base.HandleEndKey(keys);
    }
}

Workaround:
this.radVirtualGrid1.RowCount += 100;
this.radVirtualGrid1.TableElement.PagingPanelElement.UpdateView();

To reproduce:
- Remove the default padding:

private void RadVirtualGrid1_RowExpanding(object sender, VirtualGridRowExpandingEventArgs e)
{
     e.ChildViewInfo.Padding =new Padding(0,0,0,0);
 
}

Still some space remains, this can be seen in the demo application as well.

To reproduce:
void radButton1_Click(object sender, EventArgs e)
{
    this.radVirtualGrid1.CurrentCell = null;
}

Workaround:

class MyRadVirtualGrid : RadVirtualGrid
{
    protected override void CreateChildItems(RadElement parent)
    {
        base.CreateChildItems(parent);
        parent.Children.RemoveAt(0);
        var field = typeof(RadVirtualGrid).GetField("virtualGridElement", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        var element = new MyVirtualGridElement();
        field.SetValue(this,element);

        
        parent.Children.Add(element);
    }
}
class MyVirtualGridElement : RadVirtualGridElement
{
    protected override Type ThemeEffectiveType
    {
        get { return typeof(RadVirtualGridElement); }
    }
    protected override bool SetCurrentCell(VirtualGridCellInfo value)
    {
        if (value == null)
        {
            if (this.IsInEditMode && !this.EndEdit())
            {
                return false;
            }

            int row = int.MinValue;
            VirtualGridViewInfo viewInfo = null;

            if (this.CurrentCell != null)
            {
                row = this.CurrentCell.RowIndex;
                viewInfo = this.CurrentCell.ViewInfo;
            }

            if (this.CurrentCell != null && (value == null || this.CurrentCell.ViewInfo != value.ViewInfo || this.CurrentCell.RowIndex != value.RowIndex))
            {
                VirtualGridRowValidatingEventArgs e = new VirtualGridRowValidatingEventArgs(row, viewInfo);
                this.OnRowValidating(e);

                if (e.Cancel)
                {
                    return false;
                }
            }
            var currentCell = typeof(RadVirtualGridElement).GetField("currentCell", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
            currentCell.SetValue(this, value);

            if (this.CurrentCell != null)
            {
                this.EnsureCellVisible(this.CurrentCell.RowIndex, this.CurrentCell.ColumnIndex, this.CurrentCell.ViewInfo);
            }

            VirtualGridTableElement tableElement = null;

            if (this.CurrentCell != null)
            {
                tableElement = this.GetTableElement(this.CurrentCell.ViewInfo);
            }
            else
            {
                tableElement = this.TableElement;
            }
            

            if (tableElement != null)
            {
                VirtualGridRowElement rowElement = tableElement.ViewElement.GetRowElement(row);

                if (rowElement != null)
                {
                    rowElement.Synchronize(false);
                }
            }

            if (value != null)
            {
                tableElement = this.GetTableElement(value.ViewInfo);
                if (tableElement != null)
                {
                    VirtualGridRowElement rowElement = tableElement.ViewElement.GetRowElement(value.RowIndex);

                    if (rowElement != null)
                    {
                        rowElement.Synchronize(false);
                    }
                }
            }

            if (viewInfo != null)
            {
                VirtualGridRowEventArgs args = new VirtualGridRowEventArgs(row, viewInfo);
                this.OnRowValidated(args);
            }

            this.OnCurrentCellChanged(EventArgs.Empty);

            return true;
        }
        return base.SetCurrentCell(value);
    }
}

To reproduce:
- Open the attached project.
- Unselect Column3 from the list.

Workaround:
this.radVirtualGrid1.MasterViewInfo.CustomColumns.RemoveAt(0);

foreach (VirtualGridRowElement rowElement in
    this.radVirtualGrid1.VirtualGridElement.TableElement.GetDescendants(delegate(RadElement x) { return x is VirtualGridRowElement; }, TreeTraversalMode.BreadthFirst))
{
    rowElement.CellContainer.Children.Clear();
}

To reproduce:
- Change the editor to VirtualGridDropDownListEditor
- Press alpha-numeric key when the grid is not in edit mode.

Workaround:
 radVirtualGrid1.VirtualGridElement.InputBehavior = new MyBehavior(radVirtualGrid1.VirtualGridElement);

class MyBehavior : VirtualGridInputBehavior
{
    public MyBehavior(RadVirtualGridElement element) : base(element)
    {

    }
    protected override bool HandleAlphaNumericKey(KeyPressEventArgs keys)
    {
        if (!this.GridElement.IsInEditMode &&
            (this.GridElement.BeginEditMode == RadVirtualGridBeginEditMode.BeginEditOnKeystroke ||
             this.GridElement.BeginEditMode == RadVirtualGridBeginEditMode.BeginEditOnKeystrokeOrF2))
        {
            //this.GridElement.HideContextMenu();
            this.GridElement.BeginEdit();
            if (this.GridElement.ActiveEditor is VirtualGridDropDownListEditor)
            {
                string symbol = keys.KeyChar.ToString();
                var editor = this.GridElement.ActiveEditor as VirtualGridDropDownListEditor;
                var element = editor.EditorElement as RadDropDownListEditorElement;

                if ((element.AutoCompleteMode & AutoCompleteMode.Append) == AutoCompleteMode.Append)
                {
                    int index = element.AutoCompleteAppend.FindShortestString(symbol);

                    if (index == -1)
                    {
                        element.EditableElementText = symbol;
                        element.EditableElement.SelectionStart = 1;
                        element.EditableElement.SelectionLength = 0;

                        return true;
                    }
                }
               
            }
            return false;
        }

        return base.HandleAlphaNumericKey(keys);
    }
}

To reproduce: use the following code snippet and follow the steps:
public RadForm1()
{
    InitializeComponent();

    this.radVirtualGrid1.RowCount = 10;
    this.radVirtualGrid1.ColumnCount = 5;
    this.radVirtualGrid1.CellValueNeeded+=radVirtualGrid1_CellValueNeeded;
}

private void radVirtualGrid1_CellValueNeeded(object sender, Telerik.WinControls.UI.VirtualGridCellValueNeededEventArgs e)
{
    e.Value = e.RowIndex + "." + e.ColumnIndex;
}

1. Pin (left or right) 1st column
2. Scroll horizontally (to not display 2nd column)
3. Unpin 1st column
4. Scroll horizontally to display 1st column
=> 1st column is hidden, the only way to make it visible is to resize a column or the entire window

Workaround: 

 private void radVirtualGrid1_ContextMenuOpening(object sender, Telerik.WinControls.UI.VirtualGridContextMenuOpeningEventArgs e)
 {
     foreach (RadItem item in e.ContextMenu.Items)
     {
         if (item.Text == 
             RadVirtualGridLocalizationProvider.CurrentProvider.GetLocalizedString(RadVirtualGridStringId.PinMenuItem))
         {
             foreach (RadMenuItem subItem in ((RadMenuItem)item).Items)
             {
                 if (subItem.Text == 
                     RadVirtualGridLocalizationProvider.CurrentProvider.GetLocalizedString(RadVirtualGridStringId.UnpinColumnMenuItem))
                 {
                     subItem.Click-=subItem_Click;
                     subItem.Click+=subItem_Click;
                 }
             }
         }
     }
 }

 private void subItem_Click(object sender, EventArgs e)
 {
      this.radVirtualGrid1.MasterViewInfo.SetColumnWidth(0, this.radVirtualGrid1.MasterViewInfo.GetColumnWidth(0));
 }

To reproduce: use the following code snippet and try to select another cell.

public RadForm1()
{
    InitializeComponent();

    this.radVirtualGrid1.RowCount = 30;
    this.radVirtualGrid1.ColumnCount = 5;
    this.radVirtualGrid1.CellValueNeeded += radVirtualGrid1_CellValueNeeded;
      
    this.radVirtualGrid1.CurrentCellChanging += radVirtualGrid1_CurrentCellChanging;
}

private void radVirtualGrid1_CurrentCellChanging(object sender, Telerik.WinControls.UI.VirtualGridCellInfoCancelEventArgs e)
{
    e.Cancel = true;
}

private void radVirtualGrid1_CellValueNeeded(object sender, Telerik.WinControls.UI.VirtualGridCellValueNeededEventArgs e)
{
    e.Value = e.RowIndex + "." + e.ColumnIndex;
}

Workaround:

public class CustomVirtualGrid : RadVirtualGrid
{
    public override string ThemeClassName  
    { 
        get 
        { 
            return typeof(RadVirtualGrid).FullName;  
        }
    }

    protected override void OnMouseDown(MouseEventArgs e)
    {
        if (e.Button == System.Windows.Forms.MouseButtons.Left)
        {
            return;
        }
        base.OnMouseDown(e);
    }
}

To reproduce:
private void RadVirtualGrid1_EditorRequired(object sender, Telerik.WinControls.UI.VirtualGridEditorRequiredEventArgs e)
{
    switch (e.ColumnIndex)
    {
        case 1:
            {
                VirtualGridTextBoxControlEditor editor = new VirtualGridTextBoxControlEditor();
                editor.CharacterCasing = CharacterCasing.Upper;
                e.Editor = editor;
            }
            break;
    }
}

- Open the editor and try using the backspace or the arrow keys. 

Workaround:
class MyGrid : RadVirtualGrid
{
    protected override void OnKeyDown(KeyEventArgs e)
    {
        base.OnKeyDown(e);

        if (this.ActiveEditor is VirtualGridTextBoxControlEditor)
        {
            var editor = this.ActiveEditor as VirtualGridTextBoxControlEditor;
            var element =   editor.EditorElement as RadTextBoxControlElement;
            element.InputHandler.ProcessKeyDown(e);
        }
    }
    protected override void OnKeyUp(KeyEventArgs e)
    {
        base.OnKeyUp(e);

        if (this.ActiveEditor is VirtualGridTextBoxControlEditor)
        {
            var editor = this.ActiveEditor as VirtualGridTextBoxControlEditor;
            var element = editor.EditorElement as RadTextBoxControlElement;
            element.InputHandler.ProcessKeyUp(e);
        }
    }
}

To reproduce:

public Form1()
{
    InitializeComponent();

    this.radVirtualGrid1.ColumnCount = 5;
    this.radVirtualGrid1.RowCount = 20;
    this.radVirtualGrid1.CellValueNeeded += radVirtualGrid1_CellValueNeeded;
}

private void radVirtualGrid1_CellValueNeeded(object sender, Telerik.WinControls.UI.VirtualGridCellValueNeededEventArgs e)
{
    e.Value = "Data" + e.RowIndex + "." + e.ColumnIndex;
}

Workaround: use a custom ScrollableVirtualCellsContainer:

public Form1()
{
    InitializeComponent();
    this.radVirtualGrid1.CreateRowElement += radVirtualGrid1_CreateRowElement;
    this.radVirtualGrid1.ColumnCount = 5;
    this.radVirtualGrid1.RowCount = 20;
    this.radVirtualGrid1.CellValueNeeded += radVirtualGrid1_CellValueNeeded;
}

private void radVirtualGrid1_CreateRowElement(object sender, VirtualGridCreateRowEventArgs e)
{
    e.RowElement = new CustomVirtualGridRowElement();
}

private void radVirtualGrid1_CellValueNeeded(object sender, Telerik.WinControls.UI.VirtualGridCellValueNeededEventArgs e)
{
    e.Value = "Data" + e.RowIndex + "." + e.ColumnIndex;
}

public class CustomVirtualGridRowElement : VirtualGridRowElement
{
    public CustomVirtualGridRowElement()
        : base()
    {
        FieldInfo fi = typeof(VirtualGridRowElement).GetField("scrollableColumns", BindingFlags.NonPublic | BindingFlags.Instance);
        ScrollableVirtualCellsContainer scrollableColumns = fi.GetValue(this) as ScrollableVirtualCellsContainer;
        CustomScrollableVirtualCellsContainer newScrollableColumns = new CustomScrollableVirtualCellsContainer();
        FieldInfo fi2 = typeof(ScrollableVirtualCellsContainer).GetField("rowElement", BindingFlags.NonPublic | BindingFlags.Instance);
        fi2.SetValue(newScrollableColumns, this);
        this.Children.Remove(scrollableColumns);
        this.Children.Insert(1, newScrollableColumns);
    }
}

public class CustomScrollableVirtualCellsContainer : ScrollableVirtualCellsContainer
{
    protected override SizeF MeasureElementCore(RadElement element, SizeF availableSize)
    {
        int scrollOffset = 0;

        if (this.RowElement.TableElement.ColumnScroller.ScrollMode == ItemScrollerScrollModes.Discrete)
        {
            for (int i = 0; i < this.RowElement.TableElement.ColumnScroller.Scrollbar.Value; i++)
            {
                scrollOffset += this.RowElement.TableElement.ColumnScroller.GetScrollHeight(
                    this.RowElement.TableElement.ViewInfo.ColumnsViewState.GetItemSize(i));
            }
        }
        else
        {
            scrollOffset = this.RowElement.TableElement.HScrollBar.Value;
        }

        VirtualGridCellElement cellElement = element as VirtualGridCellElement;

        int itemOffset = this.RowElement.ViewInfo.ColumnsViewState.GetItemOffset(cellElement.Data);
        int itemWidth = this.RowElement.ViewInfo.ColumnsViewState.GetItemSize(cellElement.Data);

        element.Measure(availableSize);

        if (itemOffset + itemWidth > scrollOffset && itemOffset < scrollOffset)
        {
            return new SizeF((itemOffset + itemWidth) - scrollOffset, element.DesiredSize.Height);
        }

        return element.DesiredSize;
    }
}

Please refer to the attached sample project.

To reproduce:
- Subscribe to the SelectionChanged event.
- Move the mouse while holding the left button.
- The event is fire multiple times.

Workaround:
VirtualGridCellInfo prevCell = null;
private void OnGridSelectionChanged(object sender, EventArgs e)
{
    if (prevCell != gvItems.CurrentCell)
    {
        _selectionChangedCount++;
    
        tbLog.AppendText("Selection changed " + _selectionChangedCount + "\r\n");
    }
    prevCell = gvItems.CurrentCell;
}

Please refer to the attached gif file demonstrating how to reproduce the issue with the Demo application.

Workaround:

Public Class Form1
    Sub New()
        InitializeComponent()
        Me.RadVirtualGrid1.AllowAddNewRow = False
        Me.RadVirtualGrid1.AllowFiltering = False
        Me.RadVirtualGrid1.ColumnCount = 5
        Me.RadVirtualGrid1.MasterViewInfo.RegisterCustomColumn(3)     
        Me.RadVirtualGrid1.RowCount = 1
    End Sub
    Private Sub RadVirtualGrid1_CreateCellElement(sender As Object, e As VirtualGridCreateCellEventArgs) Handles RadVirtualGrid1.CreateCellElement
        Dim columnIndex As Integer = e.ColumnIndex
        If e.ViewInfo.ColumnsViewState.TopPinnedItems.Count > 0 AndAlso e.ColumnIndex - 1 < e.ViewInfo.ColumnsViewState.TopPinnedItems.Count Then
            columnIndex = e.ViewInfo.ColumnsViewState.TopPinnedItems(e.ColumnIndex - 1)
        End If

        If columnIndex = 3 AndAlso e.RowIndex >= 0 Then
            e.CellElement = New RedCellElement()
        End If
    End Sub

    Private Sub RadVirtualGrid1_CellValueNeeded(sender As Object, e As VirtualGridCellValueNeededEventArgs) Handles RadVirtualGrid1.CellValueNeeded
        e.Value = String.Format("{0}x{1}", e.RowIndex, e.ColumnIndex)
    End Sub
End Class

Class RedCellElement
    Inherits VirtualGridCellElement

    Sub New()
        MyBase.New()
    End Sub

    Private checkBox As RadCheckBoxElement
    Protected Overrides Sub CreateChildElements()
        MyBase.CreateChildElements()
        Me.checkBox = New RadCheckBoxElement()
        Me.Children.Add(Me.checkBox)
    End Sub

    Protected Overrides ReadOnly Property ThemeEffectiveType() As Type
        Get
            Return GetType(VirtualGridCellElement)
        End Get
    End Property

    Public Overrides Function IsCompatible(data As Integer, context As Object) As Boolean
        Dim headerRow As VirtualGridHeaderRowElement = TryCast(context, VirtualGridHeaderRowElement)
        If data >= 3 AndAlso headerRow Is Nothing Then
            Return True
        Else
            Return False
        End If
    End Function

    Protected Overrides Sub UpdateInfo(args As VirtualGridCellValueNeededEventArgs)
        MyBase.UpdateInfo(args)
        Me.NumberOfColors = 1
        Me.DrawFill = True
        Me.BackColor = Color.Red
    End Sub

End Class

To reproduce:
public RadForm1()
{
    InitializeComponent();
    radVirtualGrid1.CellValueNeeded += RadVirtualGrid1_CellValueNeeded;
    radVirtualGrid1.ColumnCount = 100;
    radVirtualGrid1.RowCount = 50;
    radVirtualGrid1.AutoSizeColumnsMode = Telerik.WinControls.UI.VirtualGridAutoSizeColumnsMode.Fill;
    radVirtualGrid1.SelectionMode = Telerik.WinControls.UI.VirtualGridSelectionMode.CellSelect;
}

private void RadVirtualGrid1_CellValueNeeded(object sender, Telerik.WinControls.UI.VirtualGridCellValueNeededEventArgs e)
{
    e.Value = string.Format("Col {0} Row{1}", e.ColumnIndex, e.RowIndex);
}