Comment 93 for bug 709461

I'm also experiencing this issue frequently, at random, with Unity and classic GNOME, on two different computers running up-to-date copies of 11.04. (One's a desktop with an NVIDIA display adapter and a 1280x1024 screen; the other's a netbook with integrated Intel graphics and a 1024x800 screen.)

One additional thing I noticed is that pressing Alt-Tab usually makes the dead zones disappear for a while. (This workaround is the one thing keeping me from pulling my hair out...) Maybe it's related to the Compiz Alt-Tab plugin?