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 the R1 2017 SP1 Release.

Tapping on GridViewGroupRow or GroupHeaderRow does not expand the group

RadGridView.ValidationType property will be available with R2 2016. 

The functionality is documented at http://docs.telerik.com/devtools/wpf/controls/radgridview/filtering/icolumn-filter-descriptors and for the time being the functionality can be achieved by implementing an attached behavior. 

ClipboardCopyMode enumeration will expose a new property - SkipNullOrEmptyValue - setting whether null/empty value will be copied or not. Thus if copying cells from a column with multiple empty values, will not have a result in the pasted text, but rather be skipped.