Comment 4 for bug 470604

This happened to me after a Jaunty -> Karmic upgrade. The behaviour is consistent: say you move your mouse directly downwards onto an entry in the (horizontal) list. It will change to the hover colour, and clicking on that entry will work. From here moving the mouse to the left always will have no effect (the first item will remain highlighted, left clicking no longer works), whereas moving the mouse to the right will occasionally change the focus to those items with lots of tooltip flickering, and maybe allow clicks.

Since my natural action is to run the mouse pointer along the window list, this behaviour kinda sucks. Might try the "Visual Effects" trick until this bug gets fixed.