Currently , when a RadButton has Command wired/bound, the Commands CanExecute() method's returned value is with higher priority than the IsEnabled property's value. We have previously logged this as a bug in the RadButtons and you can vote for this PITS item, this way increasing its development priority.
The only workaround is to customize your CanExecute() logic so that you don't need to use the IsEnabled property. Hope this is suitable for you.
the Telerik team
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