I would have to agree, I didn't realize that F6 and F8 worked for you. With my problem they exhibited the same symptom.
Once I can get to replacing that one HD in my RAID I can test on my systems, but that's a bit of a chore and my real job has got me working overtime lately. I honestly haven't done this before... I usually use LVM for such things, but Ubuntu doesn't use that by default so this RAID was creating using LVM. I'm going to have to do some research on the Ubuntu way to replacing a bad HD in a RAID array. I'm sure it's not incredibly difficult, it's just something I have to research and very carefully do (I'm always extra careful when it comes to my data).
But I digress... does this happen on all MD's, or is it different based on the hardware it's running on? This really does seem like an OpenGL issue, when dealing with the cursor. I remember, back in the day, I had to deal with such bugs with things blinking as the cursor moves... although I was using MS crap... still the same concept though. Basically the cursor move updated the image before, after, and as the image was "flipping" into view. In other words two things where trying to draw in the same location at the same time.