Comment 23 for bug 446425

Upstream suggests this may be due to a patch recently included, which was found to cause problems on kwin. They would like you to test reverting that patch to confirm it is indeed the source of the problem.

For your convenience, I have created a PPA for you which reverts the patch. Installing this PPA and restarting X, and then trying to reproduce the issue should be sufficient to perform the testing that upstream wants.

  https://edge.launchpad.net/~bryceharrington/+archive/black