I have the same problem, but it's easy to avoid it:
When you push the power button to suspend (or use the menu in X), just make sure you wait long enough before you resume. (about 15 seconds ?). I don't know exactly how long it is you really have to wait, but it solves the problem for me.
I think that when the screen goes blank, the Z is still busy "suspending" for a few seconds after that. If you try to resume during this suspending procedure, X freezes.
I also pushed the power button by mistake a few times, then I'm tempted to continue immediatly and X freezes. I've learned not to push the button too soon by now.
Chero.