Hi Eric & Andrew,
I can confirm that both closing the lid of the laptop (MacBook Pro) and setting the laptop display to the NEC profile (separately) "fix" the problem.
That's good info. I've passed this on to the Lr team and they're looking into a potential issue involving a primary display's profile being applied to an image being viewed (in soft proof mode) on the secondary display.
One question for you: which OS X version are you using?