Comment 60 for bug 194214

[ I've found that if I go to System > Preferences > Keyboard and uncheck "Key presses repeat when key is held down" it solves my problem. I hope that helps in figuring out whats going on. ]

I've tried this and the problem occurs anyway, I've the feeling that is when we move mouse and have a key pressed, I can be wrong.

Anyway in gutsy I didn't had this trouble, I upgrade to hardy and it happened. The problem is not young cause I had this problem on hardy alpha 2 or 3 don't remember exactly
and it was the same thing, I reinstalled gutsy to get a full working os again.

Something on Xserver is certainly the base of the problem.