I had a long talk with AppleCare about this. If you remove the DisplayLink driver, you're back to a working configuration with regard to the clamshell mode. They'll put the onus on DisplayLink. I'm guessing it's something that came out in 10.7.2 timeframe that the DisplayLink folks are tripping on. Not sure if it's an Apple fix or DisplayLink. I'm bummed that it's not fixed in 1.8 beta.