Layered windows and Windows Vista

Hi there.

Does anybody of you know about problems in Vista
when using a layered window while video overlay is in action.

I have an application where I play video with video overlay (like WMP).
Now, when I use layered windows on top of that application UI everything
starts flickering really bad. The problem seems to be gone when using
modes like DXVA or video for windows.

Is there a way to avoid this (flags, etc) ? Or is this default
behavior in windows vista ?

TIA
Mue

P.S. Another address for me where I should post this question ?