Comment 4 for bug 992516

I have this problem also. Using Ubuntu 12.04 64 bit, and Nvidia 9800GT. It happens with both proprietary Nvidia driver and Nouveau too. Screenshot http://img854.imageshack.us/img854/8371/screenshotfrom201204211.jpg

The only difference with mine is that the black glitch is only visible briefly as a flicker, and then it corrects itself. I had to be very swift to grab the screenshot above!

I hope this is useful to you. I am not versed in reporting bugs, so if there is any other information I can provide please let me know how I can provide it. Thank you.