Workaround: 
Friend Class MyRadGridView
    Inherits RadGridView

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

    Protected Overrides Function CreateGridViewElement() As RadGridViewElement
        Return New MyRadGridViewElement()
    End Function

End Class

Friend Class MyRadGridViewElement
    Inherits RadGridViewElement

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

    Protected Overrides Function CreateGroupPanelElement() As GroupPanelElement
        Return New MyGroupPanelElement()
    End Function

End Class

Friend Class MyGroupPanelElement
    Inherits GroupPanelElement

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

    Protected Overrides Function ArrangeOverride(finalSize As SizeF) As SizeF

        Dim clientRect As RectangleF = Me.GetClientRectangle(finalSize)

        Dim sizeGripRect As New RectangleF(clientRect.X, clientRect.Bottom - Me.SizeGrip.DesiredSize.Height, clientRect.Width, Me.SizeGrip.DesiredSize.Height)
        Me.SizeGrip.Arrange(sizeGripRect)
        clientRect.Height -= Me.SizeGrip.DesiredSize.Height

        Dim groupHeaderRect As New RectangleF(clientRect.X, clientRect.Y, Me.Header.DesiredSize.Width, clientRect.Height)
        Me.Header.Arrange(groupHeaderRect)
        clientRect.Width -= Me.Header.DesiredSize.Width

        Dim scrollViewRect As New RectangleF(clientRect.X + Me.Header.DesiredSize.Width, clientRect.Y, clientRect.Width, clientRect.Height)
        If scrollViewRect.Width > 20 Then
            Me.ScrollView.Arrange(scrollViewRect)
        End If

        Return finalSize

    End Function

End Class

Steps to reproduce:
1. Add RadGridView and populate with data 
2. Show the context menu many times. Sometimes the popup is not shown correctly.
If you click again, the popup is visible correctly.

Workaround: 
Set the AnimationEnabled property to false or the AnimationType property to None. Here is the code snippet how can be achieve it: 

//Set the AnimationEnabled to false
void radGridView1_ContextMenuOpening(object sender, Telerik.WinControls.UI.ContextMenuOpeningEventArgs e)
{
    RadDropDownMenu contextMenu = e.ContextMenu as RadDropDownMenu;
    contextMenu.AnimationEnabled = false;
}
 
//Set the AnimationType to None
void radGridView1_ContextMenuOpening(object sender, Telerik.WinControls.UI.ContextMenuOpeningEventArgs e)
{
    RadDropDownMenu contextMenu = e.ContextMenu as RadDropDownMenu;
    contextMenu.AnimationType = PopupAnimationTypes.None;
}

How to reproduce: check the attached video

Workaround: disable pinning of the last row when it is in a group
public partial class Form1 : Form
{
    DataTable dt;

    public Form1()
    {
        InitializeComponent();

        this.radGridView1.DataSource = this.GetData();
        this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;

        this.radGridView1.ContextMenuOpening += RadGridView1_ContextMenuOpening;
    }

    private void RadGridView1_ContextMenuOpening(object sender, Telerik.WinControls.UI.ContextMenuOpeningEventArgs e)
    {
        GridRowHeaderCellElement header = e.ContextMenuProvider as GridRowHeaderCellElement;
        if (header != null && header.RowInfo.Group != null)
        {
            var notPinned = header.RowInfo.Group.GroupRow.ChildRows.Where(r => r.IsPinned == false).ToList();
            if (notPinned.Count <= 1)
            {
                e.ContextMenu.Items.RemoveAt(0);
                e.ContextMenu.Items.RemoveAt(0);
            }
        }
    }

    private DataTable GetData()
    {
        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 < 2; i++)
        {
            for (int j = 0; j < 2; j++)
            {
                dt.Rows.Add(i, "Name " + i + " " + j, DateTime.Now.AddDays(i), i % 2 == 0);
            }
        }

        return dt;
    }
}

How to reproduce: 
public partial class Form1 : Form
{
    DataTable dt;

    public Form1()
    {
        InitializeComponent();

        this.radGridView1.DataSource = this.GetData();
        this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        dt.Clear();
        for (int i = 0; i < 100; i++)
        {
            dt.Rows.Add(i, "New Name " + i, DateTime.Now.AddDays(i), i % 2 == 0);
        }
    }

    private DataTable GetData()
    {
        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 < 500; i++)
        {
            dt.Rows.Add(i, "Name " + i, DateTime.Now.AddDays(i), i % 2 == 0);
        }

        return dt;
    }
}

Workaround:
public partial class Form1 : Form
{
    DataTable dt;

    public Form1()
    {
        InitializeComponent();

        this.radGridView1.DataSource = this.GetData();
        this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;

        this.radGridView1.RowsChanged += RadGridView1_RowsChanged;
    }

    private void RadGridView1_RowsChanged(object sender, Telerik.WinControls.UI.GridViewCollectionChangedEventArgs e)
    {
        if (e.Action == Telerik.WinControls.Data.NotifyCollectionChangedAction.Reset)
        {
            this.radGridView1.MasterView.PinnedRows.GetType().GetMethod("Clear", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)
                .Invoke(this.radGridView1.MasterView.PinnedRows, new object[] { });
        }
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        dt.Clear();
        for (int i = 0; i < 100; i++)
        {
            dt.Rows.Add(i, "New Name " + i, DateTime.Now.AddDays(i), i % 2 == 0);
        }
    }

    private DataTable GetData()
    {
        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 < 500; i++)
        {
            dt.Rows.Add(i, "Name " + i, DateTime.Now.AddDays(i), i % 2 == 0);
        }

        return dt;
    }
}

Workaround:

AddHandler Me.RadGridView1.CreateCompositeFilterDialog, AddressOf CreateCompositeFilterDialog

Private Sub CreateCompositeFilterDialog(sender As Object, e As GridViewCreateCompositeFilterDialogEventArgs)
    Dim dialog As New CompositeDataFilterForm()
    AddHandler dialog.DataFilter.EditorRequired, AddressOf EditorRequired
    e.Dialog = dialog
End Sub

Private Sub EditorRequired(sender As Object, e As TreeNodeEditorRequiredEventArgs)
    Dim filterNode As DataFilterCriteriaNode = TryCast(e.Node, DataFilterCriteriaNode)
    If filterNode IsNot Nothing AndAlso filterNode.PropertyName = "BASE_NULL_DATE" AndAlso TypeOf sender Is DataFilterValueEditorElement Then
        e.Editor = New TreeViewDateTimeEditor()
    End If
End Sub

To reproduce: please refer to the attached sample project and follow the described steps in the .doc file located in the zip. 

Workaround:

        protected override void OnActivated(EventArgs e)
        {
            base.OnActivated(e);
            this.ActiveControl = this.gvDetails;
        }

       private void gvDetails_LostFocus(object sender, EventArgs e)
        { 
            ((ComponentBehavior)gvDetails.Behavior).GetType().GetProperties(BindingFlags.NonPublic | BindingFlags.Instance);
            PropertyInfo barProperty = ((ComponentBehavior)gvDetails.Behavior).GetType().GetProperty("ScreenPresenter", 
                BindingFlags.NonPublic | BindingFlags.Instance);
            Form screenTip = barProperty.GetValue(((ComponentBehavior)gvDetails.Behavior), null) as Form;
                    
            screenTip.Hide();
        }

To reproduce: please open the attached sample project and follow the steps illustrated in the attached gif file.

Workaround: 
1. You still can scroll while dragging a row by using the mouse wheel.

2. Use the grid in unbound mode and set the AllowRowReorder property to true instead of using a custom RadDragDropService.

3. Use a custom drag and drop service:

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

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

    protected override void HandleMouseMove(System.Drawing.Point mousePosition)
    {
        base.HandleMouseMove(mousePosition);
        System.Drawing.Point location = this.GridViewElement.ElementTree.Control.PointToClient(Control.MousePosition);
        GridTableElement tableElement = this.GetTableElementAtPoint(location);

        ISupportDrag supportDrag = this.Context as ISupportDrag;
        object dataContext = supportDrag.GetDataContext();

        if (this.AllowAutoScrollRowsWhileDragging && dataContext == null)
        {
            ScrollRows(tableElement, location);
        }
    }

    private void ScrollRows(GridTableElement tableElement, System.Drawing.Point location)
    {
        ScrollableRowsContainerElement scrollableRows = tableElement.ViewElement.ScrollableRows;
        RadScrollBarElement vScrollbar = GetVeritcalScrollbar(tableElement);
        System.Drawing.Rectangle containerBounds = scrollableRows.ControlBoundingRectangle;

        if (containerBounds.Contains(location) ||
            location.X < containerBounds.X ||
            location.X > containerBounds.Right)
        {
            return;
        }

        int delta = 0;

        if (location.Y > containerBounds.Bottom)
        {
            delta = location.Y - containerBounds.Bottom;
        }
        else if (location.Y < containerBounds.Y)
        {
            delta = location.Y - containerBounds.Y;
        }

        if (delta != 0 && vScrollbar.Visibility == ElementVisibility.Visible)
        {
            vScrollbar.Value = ClampValue(vScrollbar.Value + delta,
                vScrollbar.Minimum,
                vScrollbar.Maximum - vScrollbar.LargeChange + 1);
        }
    }

    private int ClampValue(int value, int minimum, int maximum)
    {
        if (value < minimum)
        {
            return minimum;
        }
        if (maximum > 0 && value > maximum)
        {
            return maximum;
        }
        return value;
    }

    private RadScrollBarElement GetVeritcalScrollbar(GridTableElement tableElement)
    {
        if (GridViewElement.UseScrollbarsInHierarchy)
        {
            return tableElement.VScrollBar;
        }
        return GridViewElement.TableElement.VScrollBar;
    }
}

public RadForm1()
{
    InitializeComponent();
    CustomDragDropService customService = new CustomDragDropService(radGridView1.GridViewElement);
    radGridView1.GridViewElement.RegisterService(customService);
}

To reproduce: please refer to the attached sample project. Note that the CellValidating event is fired twice even without showing a RadMessageBox. With an MS Button the problem is not reproducible.

Workaround: use the RadGridView.ValueChanging event to perform validation while the user is typing in the active editor:
 private void radGridView1_ValueChanging(object sender, Telerik.WinControls.UI.ValueChangingEventArgs e)
 {
   if (((string)e.NewValue) != "x")
     {
         RadMessageBox.Show("Only 'x' allowed!");
         e.Cancel = true;
     }
 }

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

Workaround: use the CellFormatting event and apply the light orange BackColor for the selected cells belonging to the current pinned column:

private void radGridView1_CellFormatting(object sender, Telerik.WinControls.UI.CellFormattingEventArgs e)
{
    if (e.Row.IsSelected && e.Column.IsCurrent)
    {
        e.CellElement.BackColor = Color.FromArgb(255, 231, 174);
    }
    else
    { 
        e.CellElement.ResetValue(LightVisualElement.BackColorProperty, ValueResetFlags.Local);
    }
}

Use attached project to reproduce!

Another case is when the font size is changed from the settings dialog - in this case, the row height is not adjusted.

Workaround:
Use the following custom print style:

class MyTableViewDefinitionPrintRenderer : TableViewDefinitionPrintRenderer
{
    public MyTableViewDefinitionPrintRenderer(RadGridView grid) : base(grid)
    {

    }
    protected override int GetDataRowHeight(GridViewRowInfo row, TableViewRowLayoutBase rowLayout)
    {
        int result = base.GetDataRowHeight(row, rowLayout);

        int newHeight = 0;

        if (!(row is GridViewGroupRowInfo))
        {
            foreach (GridViewColumn col in row.ViewTemplate.Columns)
            {
                if (col is GridViewRowHeaderColumn || col is GridViewIndentColumn || !col.IsVisible)
                {
                    continue;
                }

                string value = row.Cells[col.Name].Value.ToString();

                TableViewCellArrangeInfo info = ((TableViewRowLayout)rowLayout).LayoutImpl.GetArrangeInfo(col);
                float cellWidth = (float)info.CachedWidth;
                int currentHeight = TextRenderer.MeasureText(value, this.GridView.PrintStyle.CellFont, new Size((int)cellWidth, 0), TextFormatFlags.WordBreak).Height + this.GridView.Font.Height *4;

                newHeight = Math.Max(newHeight, currentHeight);

            }
        }


        return Math.Max(newHeight, result); 
    }
}
class MyPrintStyle :GridPrintStyle
{
    protected override BaseGridPrintRenderer InitializePrintRenderer(RadGridView grid)
    {
        return new MyTableViewDefinitionPrintRenderer(grid);
    }
}

To reproduce:
private void RadGridView1_KeyPress(object sender, KeyPressEventArgs e)
{
    int startIndex = radGridView1.CurrentRow.Index +1;

    for (int i = startIndex; i < radGridView1.Rows.Count; i++)
    {
        var value = radGridView1.Rows[i].Cells["Name"].Value.ToString().ToLower();
        if (value.StartsWith(e.KeyChar.ToString()))
        {
            radGridView1.TableElement.ScrollToRow(radGridView1.Rows[i]);
            radGridView1.ClearSelection();
            radGridView1.Rows[i].IsSelected = true;
            radGridView1.Rows[i].IsCurrent = true;
            radGridView1.Columns[1].IsCurrent = true;
            break;
        }
    }
}

- Press some key so the grid is scrolled down, then press the down key.
- The first row is selected instead of the next one. 

Workaround:
remove this line:
radGridView1.Rows[i].IsSelected = true;

To reproduce:
1. Run the attached sample project.
2. Right-click the grid.
3. Quickly navigate to another application (e.g. Windows Explorer) before the context menu is shown & wait at windows explorer to display the menu
4. The context will be stuck.

To reproduce: run the attached sample project and you will notice that the top border is missing as it is illustrated in the screenshot. 

Workaround:  set the RadGridView.AutoSizeRows property to false.

To reproduce:
public RadForm1()
{
    InitializeComponent();
    radGridView1.DataSource = GetTable();
    GridViewSummaryItem summaryItem = new GridViewSummaryItem();
    summaryItem.Name = "Name";
    summaryItem.Aggregate = GridAggregateFunction.Count;
    GridViewSummaryRowItem summaryRowItem = new GridViewSummaryRowItem();
    summaryRowItem.Add(summaryItem);
    this.radGridView1.SummaryRowsBottom.Add(summaryRowItem);

    radGridView1.ViewCellFormatting += RadGridView1_ViewCellFormatting;
}

private void RadGridView1_ViewCellFormatting(object sender, CellFormattingEventArgs e)
{
    if (e.CellElement is GridSummaryCellElement)
    {
        e.CellElement.DrawFill = true;
        e.CellElement.GradientStyle = Telerik.WinControls.GradientStyles.Solid;
        e.CellElement.BackColor = Color.Red;

    }
    else
    {
        e.CellElement.ResetValue(LightVisualElement.BackColorProperty, Telerik.WinControls.ValueResetFlags.Local);
        e.CellElement.ResetValue(LightVisualElement.GradientStyleProperty, Telerik.WinControls.ValueResetFlags.Local);
        e.CellElement.ResetValue(LightVisualElement.DrawFillProperty, Telerik.WinControls.ValueResetFlags.Local);
    }
}

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);
    radGridView1.MasterView.SummaryRows[0].PinPosition = PinnedRowPosition.Bottom;
}

static DataTable GetTable()
{

    DataTable table = new DataTable();
    table.Columns.Add("Dosage", typeof(int));
    table.Columns.Add("Drug", typeof(string));
    table.Columns.Add("Name", typeof(string));
    table.Columns.Add("Date", typeof(DateTime));

    for (int i = 0; i < 5; i++)
    {


        table.Rows.Add(25, "Indocin", "David", DateTime.Now);
        table.Rows.Add(50, "Enebrel", "Sam", DateTime.Now);
        table.Rows.Add(10, "Hydralazine", "Christoff", DateTime.Now);
        table.Rows.Add(21, "Combivent", "Janet", DateTime.Now);
        table.Rows.Add(100, "Dilantin", "Melanie", DateTime.Now);
    }
    return table;
}
private void radButton1_Click(object sender, EventArgs e)
{

    radGridView1.SaveLayout("test.xml");
}

private void radButton2_Click(object sender, EventArgs e)
{
    radGridView1.SummaryRowsBottom.Clear();
    radGridView1.SummaryRowsTop.Clear();
    radGridView1.LoadLayout("test.xml");
}

To reproduce:
this.radGridView1.MultiSelect = true;
this.radGridView1.SelectionMode = Telerik.WinControls.UI.GridViewSelectionMode.CellSelect;

radGridView1.ShowRowHeaderColumn = false;

Then select the cells in the firs column by dragging the mouse.

Workaround:
// radGridView1.ShowRowHeaderColumn = false;
radGridView1.TableElement.RowHeaderColumnWidth = 0;

Workaround: handle the GridViewPdfExport.CellFormatting event and apply the column`s format string

Public Class Form1
    Sub New()

        InitializeComponent()

        Me.RadGridView1.DataSource = Me.GetData()
        Me.RadGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill

        Dim decimalColumn = DirectCast(Me.RadGridView1.Columns("Money"), GridViewDecimalColumn)
        decimalColumn.DecimalPlaces = 0
        decimalColumn.FormatString = "{0:C0}"

        Dim dateTimeColumn = DirectCast(Me.RadGridView1.Columns("Date"), GridViewDateTimeColumn)
        dateTimeColumn.FormatString = "{0:D}"

    End Sub

    Private Function GetData() As Object
        Dim dataTable As New DataTable()
        dataTable.Columns.Add("Id", GetType(Integer))
        dataTable.Columns.Add("Name", GetType(String))
        dataTable.Columns.Add("Money", GetType(Decimal))
        dataTable.Columns.Add("Date", GetType(DateTime))

        For i As Integer = 0 To 999
            dataTable.Rows.Add(i, "Name " & i, i * 10, DateTime.Now.AddDays(i))
        Next

        Return dataTable
    End Function

    Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
        Dim pdfExporter = New GridViewPdfExport(Me.RadGridView1)
        AddHandler pdfExporter.CellFormatting, AddressOf pdfExporter_CellFormatting
        Dim renderer = New PdfExportRenderer()
        Dim fileName As String = "..\..\exported-grid.pdf"

        pdfExporter.RunExport(fileName, renderer)
    End Sub

    Private Sub pdfExporter_CellFormatting(sender As Object, e As PdfExportCellFormattingEventArgs)
        If e.RowIndex > -1 Then
            e.CellElement.Text = TryCast(RadDataConverter.Instance.Format(e.Row.Cells(e.ColumnIndex).Value, GetType(String), e.Column), String)
        End If
    End Sub

End Class

How to reproduce:
public partial class Form1 : Form
{
    private RadGridView grid = new RadGridView();

    public Form1()
    {
        InitializeComponent();

        Controls.Add(grid);
        grid.Dock = DockStyle.Fill;
        grid.DataSource = this.GetData();
    }

    private object GetData()
    {
        DataTable dataTable = new DataTable();
        dataTable.Columns.Add("Id", typeof(int));
        dataTable.Columns.Add("Name", typeof(string));
        dataTable.Columns.Add("Checked", typeof(bool));

        for (int i = 0; i < 200; i++)
        {
            dataTable.Rows.Add(i, "Name " + i, i % 2 == 0);
        }

        return dataTable;
    }

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);

        grid.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;

        GridViewCheckBoxColumn checkBoxColumn = (GridViewCheckBoxColumn)grid.Columns["Checked"];
        checkBoxColumn.EnableHeaderCheckBox = true;
        checkBoxColumn.SortOrder = RadSortOrder.Ascending;
    }
}

Workaround: 
public partial class Form1 : Form
{
    private RadGridView grid = new RadGridView();

    public Form1()
    {
        InitializeComponent();

        Controls.Add(grid);
        grid.Dock = DockStyle.Fill;
        grid.DataSource = this.GetData();

        grid.MouseDown += grid_MouseDown;
        grid.MouseUp += grid_MouseUp;
    }

    private object GetData()
    {
        DataTable dataTable = new DataTable();
        dataTable.Columns.Add("Id", typeof(int));
        dataTable.Columns.Add("Name", typeof(string));
        dataTable.Columns.Add("Checked", typeof(bool));

        for (int i = 0; i < 200; i++)
        {
            dataTable.Rows.Add(i, "Name " + i, i % 2 == 0);
        }

        return dataTable;
    }

    private void grid_MouseDown(object sender, MouseEventArgs e)
    {
        RadGridView grid = (RadGridView)sender;
        RadCheckBoxElement cell = grid.ElementTree.GetElementAtPoint(e.Location) as RadCheckBoxElement;
        if (cell != null && cell.Parent is GridCheckBoxHeaderCellElement)
        {
            sw = new Stopwatch();
            sw.Start();
            grid.BeginUpdate();
        }
    }

    Stopwatch sw;
    private void grid_MouseUp(object sender, MouseEventArgs e)
    {
        RadGridView grid = (RadGridView)sender;
        RadCheckBoxElement cell = grid.ElementTree.GetElementAtPoint(e.Location) as RadCheckBoxElement;
        if (cell != null && cell.Parent is GridCheckBoxHeaderCellElement)
        {
            grid.EndUpdate();
            sw.Stop();
            Console.WriteLine(sw.ElapsedMilliseconds);
        }
    }

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);

        grid.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;

        GridViewCheckBoxColumn checkBoxColumn = (GridViewCheckBoxColumn)grid.Columns["Checked"];
        checkBoxColumn.EnableHeaderCheckBox = true;
        checkBoxColumn.SortOrder = RadSortOrder.Ascending;
    }
}

To reproduce: please refer to the attached sample project and follow the steps in the provided gif file: 
1. Enter something in the search bar
2. Filter on some column, uncheck "All", then select a few items, then validate
3. Click on a random row on the grid
4. Filter on the same column as in 2., check "All", then uncheck a few items, then validate

Workaround:

private void radGridView1_FilterChanged(object sender, Telerik.WinControls.UI.GridViewCollectionChangedEventArgs e)
{
    this.radGridView1.MasterTemplate.Refresh();
}