I have nearly the same problem as you.
When I'am view TV with my Cinergy T2 (USB device/DVT-T) from Terratec with Kaffeine or Xine everything is fine. But I'm starting another movie or starting a simple 3D game like Chronium, the TV is going mad.
It doesn't matter if I'm using 8774 or 9625 or a fresh Suse 10.1 system, the result is always the same.
I have corrupt MPEG even if kaffeine is not running but Chromium B.S.U. or FooBillard is started.
Interesting: I don't have corrupt MPEG stream if the Chrominum window is only 640x480. With 800x600 I have some bad pictures and with 1024x768 it's worst.
I'm NOT running compix/glx.
Any idea, how to record TV via DVB-T AND watching other movies or playing games?