Since the FlowDirection of the CheckBox is set to RightToLeft the check path is reversed indeed.
You may see the same behavior with a single CheckBox with the following settings:
If you want to override this behavior in RadGridView's FilteringControl you may predefine its template and harcode the FlowDirection of the CheckBox in the LIstBox, which holds the DistinctValues.
I am attaching you sample project and a picture which demonstrates this approach.
All the best,
the Telerik team
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