If you need your validation on uncheck to work only for the item you have tried to uncheck with your mouse, you have to use the IsUserItnitiated property like so:
sender, Telerik.Windows.RadRoutedEventArgs e)
isInitiallyChecked = (e
(isInitiallyChecked && ((e.OriginalSource
You can find this realized in the attached sample. Please let us know if this helps you or not.
the Telerik team
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