Ubuntu :: "Dead" Space, Can't Click There?

This has been consistent with all 4 of my Ubuntu installs (1 wubi, 1 minimal, 2 full cd). Of note, it's on the same machine, but on 2 different hard drives and with various configurations of different hard drives being plugged/unplugged. I apologize for the terrible drawing but it should get the point across. That space about a third of the way up, clicking in it does nothing. The cursor doesn't change whether it's over a link or text or a file or anything. The spot hasn't moved over 4 installations. I don't even know what to google... (I'm just assuming it's a rectangle like that from moving my mouse around it, there's nothing actually on the screen to indicate that there's an actual thing in the area preventing me from clicking.) Weird! And incredibly annoying, I've never heard of anything like this. Has anyone had this problem, if so how was it solved?