OS X Guest Keyboard Freezing

Using Fusion 5.0.3.

My OS X guests (10.8.3) have an issue where the keyboard freezes sometimes.  It's not very often.  But I've experienced it twice in one week now.

When this happens, the mouse still responds.  The system is still responsive.  I just have to use the mouse to do a system restart.  Then when it comes back up the keyboard is good again.

Is there some setting I can change to fix this?  Or a way to recover without rebooting?

Thanks!

~Daniel