I've already asked this on the IMUG list (thanks Floh for you comments), but thought I might learn more here:
So, here's something a bit strange...
M100 v8 timeline.
PAL Digibeta material digitised via SDI.
EDL exported to 844x and redigitised for finishing.
Audio mix exported as AIFF from M100 and imported into 844x. Line up the exported AIFF audio file with the re-dig'd edit in 844x via SDI. It won't fit! It's half a frame out... Or, in other words, a field out! You can only line up the AIFF (visualised by the waveform) half a frame before or after the re-dig'd audio (which is perfectly in sync with the video).
The only thing I can think of is some sort of field order conflict between the M100 & 844x.