This Bug Affects me too, however for me this Bug occured on Ubuntu 13.04 Unity Beta Freeze Build (03-28-2013) with all Bug Fixes installed on 03-31-2013 (Easter Sunday), bug occured right after updating 13.04 to Mainline Kernel 3.8.5 and then Rebooting the Computer.
This Bug Affects me too, however for me this Bug occured on Ubuntu 13.04 Unity Beta Freeze Build (03-28-2013) with all Bug Fixes installed on 03-31-2013 (Easter Sunday), bug occured right after updating 13.04 to Mainline Kernel 3.8.5 and then Rebooting the Computer.