Okay. So previously, I thought this was a compiz issue, but then I switched to metacity, and noticed it happened with Totem too. So I think this is an nVidia issue...
There's the green and purple bars that show up. With Compiz, they go crazy and appear all around wobbly windows and everywhere.

[screenshot]

Any suggestions on what to do? It's so very annoying. >.<
I'm using an nVidia GeForce 7300 LE with restricted drivers.