Issue assigning group expand/collapse state by code

I'm attempting to maintain the expand/collapse state of a grouped DataGrid.

The issue I'm facing is that as soon as I set the state of args.Expanded within OnGroupRowRender, I lose the ability to toggle the state via the GroupExpandColumn.

It appears that void OnGroupRowCollapse(Group group) and void OnGroupRowExpand(Group group) completely cease to function.

Is this a bug?