Hello, 

I believe that the issue is not a trivial one and depends on the data inside the FilteringControl. I will explain the current status - in our older themes such as Office Black and Expression Dark, the filtering control has fixed width which leads to such clipping when default FontSize is changed. In our latest themes, it has MinWidth set, which in some cases leads to Popup jumping on scrolling. As you see there is no ideal solution. From the ticket provided, I see that in your scenario the data is homogeneous and with similar length. That is why I think that the suggested approach for fixing the issue locally by setting a custom style with setter for the Width to Auto is appropriate. However it is not applicable for all possible scenarios. 

Regarding the fixed height of the RadButtons, it is a mistake in the implementation of the themes and will be fixed. You will be notified when its status is changed to "In Development".

All your feedback would be appreciated. 

Regards, 
Sia