So I did a bit of fiddling:
For me, it's definitely not software related. I tested on Mac OS X (on another QS), and it worked fine. Then, I went back to test it on the 9.2.2 machine, and it worked. Briefly.
The brightness would occasionally disappear out of the control panel, and USB devices would occasionally disconnect. I honestly think it's just a flaky connector.
Next thing to try is to swap the two graphics cards, see if the connector from the card in the OS X machine is any better.