Indeed, we have introduced breaking changes with the Q1 2012 version of the Controls. Please check here for detailed information on all the changes done.
The changed code, in your case, would look like so:
Simply calling RadGridView.FilterDescriptors.Clear will indeed remove the filtering, but the column filters will preserve their settings (although they will not be part of the FilterDescriptors collection). To completely clear a column filter you have to call column.ClearFilters();
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