cannot leave gnome-shell screen lock after authenticating

Hi,
I have Ubuntu 12.10 with gnome-shell installed over default Unity desktop. I have an windows app that I run under vmware player and VirtualBox. With both of them I experience the same problem:

When computer is idle, gnome screen gradually darkens and locks the screen. It is configured to require password for unlocking the session. Hovever, when VMware or VirtualBox is running on full screen, user is unable to unlock the screen after entering correct password. Instead, user sees dark-gray gradient screen with locked icon on top left corner and accessibility options in top-right corner of gnome bar.

What is interesting Alt-F2 works and allows to execute programs but they will launch hidden "under the lock screen". Also it IS possible to unlock the desktop. Just not sure how. Switching between other displays with another user (Alt-F7, Alt-F8) did once make this lock screen give up and show desktop with apps (It may have even crashed as ram was getting low then).

How to recover GDM session or prevent screen lock from misbehaving? I do not want to restart GDM and loose data.

How to figure out which process is to blame so I can make sure it does not run or kill it? I believe it cannot be full-screen apps fault, as desktop manager should protect session just like OS protects from segfaulting processes.