Comment 3 for bug 966122

I am seeing the exact same thing, and have so for a while. From what I can tell it has to do with Chrom{e,ium} 18.x and notifications. The white box appears when I have a gmail notifications specifically. I have been seeing this for a while, and have been trying to figure it out. From what I can tell it is not a window as you can click through it and I can't use Alt-grab to move it. It simply seems to be a region of the screen that won't repaint. Video memory corruption? Ah, I also noticed it has a drop shadow, so it kind of acts like a window - or maybe compiz is simply treating it as one.

For troubleshooting I exited Chromium (18.x) and the white rectangle doesn't go away. Even exiting all apps doesn't make it go away. It does go away if I logout and back in again. I then installed the stable version of Chrome (which was at the time 17.x). I didn't see this for a while, but it returned when Chrome was upgraded to 18.x. Further, I noticed it appears after a gmail notification comes up. Specifically, I had several gmail notifications appears in a row and the white rectangle appeared. I exited Chrome, logged out and back in again and tried to reproduce by having several people ping me in IRC (I am using a web-based irc client) but couldn't make the rectangle appear. This morning I got a single notification from gmail and the white rectangle appeared.

This appears to me to be a problem with Chromium, but I'm struggling to get good troubleshooting information as I can't get any information on the "window".