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I thought this might have been just my application at first, but I have been able to replicate it in your demo environment...
http://demos.telerik.com/silverlight/#GridView/FirstLook
Add two groups to the grid (I picked "Title" and "City" but it doesn't seem to matter). Remove the first group and notice that the arrow pointing to the second group is still visible. I'm not sure if this is something that appeared after the recent QA release or not.
http://demos.telerik.com/silverlight/#GridView/FirstLook
Add two groups to the grid (I picked "Title" and "City" but it doesn't seem to matter). Remove the first group and notice that the arrow pointing to the second group is still visible. I'm not sure if this is something that appeared after the recent QA release or not.