First, sorry about the late reply, I've been very busy with something else.
Your sample solves some issues, but there are still some problems. I wanted to check what happens with more than one item per group (but still more than one group), so I modified one method this way:
ID = index,
Age = 20,
+ (index % 4 + 1),
JobCode = 1000 + index,
Note the "Name" line. This way I have 5 items per group when grouping by Name. Every time I use the checkbox on the Group header everything works well, the problem comes when I individually select or unselect an item, the group's checkbox isn't refreshed. The result is the attached image.
Basically, I need a way to receive a message every time an item selection changes from every group. Easier said than done. Maybe a mix of events and attached properties? I don't mind inheriting RadGridView if I must, in fact, I've already done so.
EDIT: I attached a different image than intended and I can't remove an attachment. The correct file is "GroupRefreshProblem.png".