I was playing a track on my MB Air and while it was playing, I clicked on the output zone, which brought up the list of available zones that it detected (that were not enabled). I enabled the AirPort Express zone it detected, it prompted me for the password and it connected / switched output. The checkbox switched to the AirPort Express zone, but it was flickering rapidly and output kept continuing on the system zone (speakers). If I clicked back on the system zone it the checkbox kept flickering rapidly and playback continued. No matter what I clicked on the checkbox was stuck in some sort of update loop and playback was never interrupted.
In addition to the above issue, the AirPort password entry was in clear-text and not obscured. By default you should obscure the password text entry.