Comment 6 for bug 785681

Sergio Callegari, while the original reporter wasn't using either Kubuntu, or a nvidia graphics card, given how old this report is, it is likely you are experiencing a completely different problem with a different root cause.

Hence, it will help immensely if you use the computer the problem is reproducible with, file a new report with Ubuntu by first ensuring the package xdiagnose is installed, click the Yes button for attaching additional debugging information after running the following from a terminal:
ubuntu-bug xorg

Also, please feel free to subscribe me to it.