Since the last update (to Build 9.0.23062), the windows screen will go black after switching to another OS X user while the VM is running and back. The only solution to get back the screen is shutting down/rebooting the VM.
Running Mavericks 13A584, Windows 8.1 RTM in the VM. I also use two screens.
Running Mavericks 13A584, Windows 8.1 RTM in the VM. I also use two screens.