This happens to me on 12.10. And also blank windows - not just visually blank, you can actually see through them, i.e. if you move them, the image you see is not frozen, also you can click through.
This happens to me on 12.10. And also blank windows - not just visually blank, you can actually see through them, i.e. if you move them, the image you see is not frozen, also you can click through.