Hi,
I'm running Linux 3.2.5 with VirtualBox 4.1.8. Since a few days now, I have the problem that my Windows 7 guest is extremely unstable at certain times.
The Windows guest reboots. Or it shows screen corruptions. Miktex randomly fails to install (files integrity issues). VBox log doesn't show anything oviously suspecious.
I'm under the impression, it might have something to do with suspend to RAM. When I reboot my Linux host, the Windows guest is more stable than usual.
I also had the WDDM graphics driver installed. But I uninstalled Guest additions and reinstalled them without. Also, 3D acceleration and 2D acceleration is disabled for the Windows guest. I reduced the number of CPUs of the guest to 1, just to be safe.