I've noticed another issue while using the recent nvidia drivers (185 and above) and mythtv. I was wondering if you can check if you have the same effects.
Here's what's happening: If I run mythtv (watching TV) and open another program on top of that (say firefox), black areas in firefox seem to be transparen, showing the image from mythtv.
Have a look at this post
where I attached a picture that shows this effect.
Are you able to reproduce this ? I'm running 8.10, ffmpeg for decoding and vdpau for rendering