Blank screen when coming back to X(compiz) after switching to text console

[ale1612]

When I use compiz, if I switch to another virtual text console all works fine but when I switch back to X console the sceen is blank and the only thing I can see is the mouse pointer.
I can still control the mouse pointer, sometimes I can switch again back to text console but usually the system does not react to any keystroke (I tried ctla-alt-F1, ctrl-alt-backspace and cntrl-alt-del).
However the system is not hanging, I can connect via ssh from a remote PC.

The problem doesn't happen if I don't enable compiz.

I'm using Debian Etch and nvidia driver 9631 (GeForce4 Ti 4200).

I attach the file nvidia-bug-report.log after the blank screen happened.