Unfortunately I'm out of ideas what's going on in your case. If this collection will work normally with standard Silverlight components like ListBox, DataGrid, etc. and will not work with RadGridView, please open support ticket and send us small project demonstrating your scenario. We will review your implementation and we will get back with more info.
the Telerik team
Explore the entire Telerik portfolio by downloading the Ultimate Collection trial package. Get it now >>