Well, it was always problematic before 10.8.3, now it doesn't even pretend to work. No refreshes. At all. I have to move my mouse over the portions of the screen that would be refreshed (iStat, Drobo Dashboard, etc) to see just that tiny sliver. Setting 'full screen' or 'full quality' does not change the issue. FYI- The mini in question is a 2012 i7 Server with 10.8.3 installed connected to my iMac via Thunderbolt cable (F2 for Target Display Mode).