The issue seems to be a bug with UI Row Virtualization since once I set it to False, it did not occur any more. You can also refer to the documentation on UI Virtualization: http://docs.telerik.com/devtools/wpf/controls/radgridview/features/ui-virtualization.html

When tabbing in grouped RadGridView placed in Grid with another visual element inside it, GroupRenderMode is set to Flat  and second group is not in ViewPort, selected row changed its state to Unfocused.

Application hangs on start up if GroupRenderMode is set to Nested, there is a column with Width Star and a group descriptor applied.

You can not select different filtering options through keyboard navigation. The only possible way to select a filtering operator from the list with available filtering operators is to click on it.