Comment 10 for bug 990069

It happened to me. It seems that it has to be something with the new unity settings for compiz after upgrade from 11.04 or 11.10. I've found a workaround restoring unity's default settings by running unity --reset. This restores to the original settings, so if you've made a lot of changes with the ccsm (like me) it will be LOST. If you have enough patience, you can apply all of your changes back. It worked for me.