If you have a RadComboBox inside a ControlPanelItem, when you open the RadComboBox's dropdown and select an item, the ControlPanelItem is not closed. As a workaround, you can manually capture the mouse. Please check the attached project.

A possible workaround is to show and hide the columns.

foreach (GridViewColumn col in TestGridView.Columns)
			{
				bool visibility = col.IsVisible;
				col.IsVisible = true;
				col.IsVisible = visibility;
			}

Grouping of columns in RadGridView by using a ColumnGroupDescriptor in XAML does not work when ShowGroupPanel is set to False and there is a RelativeSource binding in the ColumnGroupDescriptor.

A NullReferenceException can be thrown when quickly editing different cells with a RadMultiColumnComboBox (placed in the CellEditTemplate of the column) and changing the selection. 

System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=Telerik.Windows.Controls.GridView
  StackTrace:
   at Telerik.Windows.Controls.MultiColumnComboBox.GridViewDropDownContentManager.OnMouseUp(Object sender, MouseButtonEventArgs args) in Telerik.Windows.Controls.MultiColumnComboBox\GridViewDropDownContentManager.cs:line 283

Expecting the popup to be kept open, its zorder is still on top of the grid it is linked on, but not on top of other applications whose zorder is closer to the user than the application window containing the grid.

GridViewColumnGroups.Header does not respect any content different from string when EnableColumnGroupsVirtualization is True.

*** Workaround: Use HeaderTemplate property instead or set EnableColumnGroupsVirtualization to False in all themes different than Windows8, Windows8Touch and ExpressionDark.

The problem should be resolved with version Q2 2015 SP1.

WinForms: http://www.telerik.com/help/winforms/gridview-grouping-setting-groups-programmatically.html

You can find our online documentation on a detailed information on the currently supported grouping:
http://docs.telerik.com/devtools/wpf/controls/radgridview/grouping/basics.html

Available in LIB version 2018.1.122, it will be also available in the R1 2018 SP Release.

Available in the R1 2017 SP1 Release.

Tapping on GridViewGroupRow or GroupHeaderRow does not expand the group

The fix is available in the R1 2018 Release.