Thanks for the tipoff guys!
Yes, but I continue to be stupid. This time, I had a bare-bones QApplication I had just written. Added a few lines to the MainWindow constructor to set some things up (pushing std:: wstring constants onto a std:: vector< std:: wstring > >) and it kept crashing with a heap corruption error. After another wasted hour, discovered it was a mismatch of release and debug libraries yet again.

This nasty bug keeps appearing in different disguises. I guess the take-away lesson is that if you have perfectly good code that won't run, it has nothing to do with the code, it's the way you're building it. Hopefully I'll be quicker to realize that next time.