Comment 5 for bug 1097118

Please repeat B many more times and attach the result.

Also, it looks like the problem might be your graphics driver: fglrx, 9.002. This is not a version officially supported by Ubuntu so please uninstall it and either:
(a) use the default built-in radeon driver; or
(b) install a supported version of fglrx via:
   gnome-control-center > Software Sources > Additional Drivers