This behavior is expected, as when the ItemsSource of a RadGridView is changed, there is no guarantee that the columns and descriptors defined will be applicable to the type of the new data items. That is why, rather than risking exceptions in the LINQ runtime, they are cleared. You can have a look at a couple of similar threads discussed here
One solution I can offer is to save the group/sort descriptors somewhere before resetting the data and add them to the GroupDescriptors/SortDescriptors collection after the data has come.
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