I searched a bit and found some similar issues described but nothing exactly like this... and none of the suggestions in them really applied.
I'm having a weird issue with a specific machine running KDE. Clean and updated install of Kubuntu 11.10. nvidia 5500 graphics card. I am able to run desktop effects, but there is visual corruption. I changed the compositing to xrender, which fixes the corruption but I can't do half the effects and it's much slower / laggier than opengl.
Here's a picture of what happens when I enable opengl:
I haven't seen this issue with My other computers, so I'm not sure what I could check. I have the nvidia 173 drivers installed via "additional drivers" and it says it's activated. Opengl enables with no errors and runs smoothly, with the exception of the visual corruption.