In a Ubuntu Natty desktop PC I connect to a MS Windows machine via Citrix Receiver, sometimes window looks weird (has blank areas, yo have to switch to another window outside citrix and come back to see it right). I tried wfcmgr changing window color settings but no luck. I think it's related with graphics card (ATI), changing to Ubuntu classic with no effects (no Unity, no Compiz) solves the problem but I don't want to stay in Ubuntu classic.
Now i'm using Unity 2D and works fine for me so seems a compiz related problem.