I have a MacBook Pro with a RV530 with an external Philips 22" monitor
connected (the notebook screen is disabled in X). After switching to VT and
then coming back to X the screen is corrupted (like if every odd line has an
offset). The same happens after suspend. A screenshot doesn't show the problem.
I then usually change resolution with the Ubuntu tool (selecting a different
resolution and then reapplying the previous one) and that restore the screen.

Attached dmesg and Xorg log after the X -> VT -> X cycle.