Using sample non square pixel tests from Microsoft site was inconclusive.
7 of the 27 sample encoded videos were 1:1 PAR. The others varied from 24:11 to 12:11
None of the videos played past the first frame, but all the videos was missing an audio track and I’m not sure if that had something to do with it.
Once again – the videos played normally under Windows Media player 11.
So this sheds a little more light on the problem – I know there is an issue, but the pattern is elusive.