To answer the various questions:
PandaUK - It did display N, and the buzzer buzzed too. I've had the 'gearbox fail' too, again a couple of times within a few minutes, but only once a few months ago
T14086 - Traffic lights seem to be on red for ages these days, but no way was it five minutes.
ahhl - thanks for the info, odd thing is that I've done this same journey lots of times and never noticed it happen before. I don't put it into neutral at traffic lights etc - should I?