This bug was one of main reasons that I stopped using Unity in 11.04 and went back to Gnome 2. After upgrade to 11.10, it kind of dissapeared, showing only occasionaly, but in the last couple of days (maybe after some of the updates) it became again very annoying. I minimize/maximize Firefox at least once in 20 minutes (or, when that doesn't work, close it and start again). It really goes on my nerves, but, alas, I cannot go back to Gnome 2, nor use Gnome Shell (it still has issues with my Radeon card). Unity 2D, last time I tried, didn't have all the features of 3D version (and I don't mean eye-candy). Mint (debian) anyone?