I've confirmed through a few other sources, and with a bit of trial-and-error of my own that this is related to Auto-Hide on x64 Windows 7 Systems, hardware doesn't seem to come into play. For me it happened on two different computers, one a laptop with no common hardware manufacturer, and the other a desktop system I built last summer.
For now it seems disabling 'auto hide the taskbar' fixes the problem. I hate this though, so I've found that if you leave a window open, or your mouse-over the task bar it should be 100% fine.
I hope Microsoft figures the issue out on their end and patches it soon. It's annoying, and I don't always remember to leave a window open (on screen, not minimized). Additionally I have a habit of hitting the show desktop button before leaving my system.
My two-cents might be pointless at this point, but I thought I'd throw them into the hat anyway. Similar issues may be caused by other things, but an issue that matches the description of the TC is consistently experienced by many users who 'auto-hide' their taskbar.