I have a memory of seeing the exact same issue you report, in FCP 4 or 5 some years ago. At that time I solved it by examining the source clips. I found some to be MP3 clips, which I converted to AIF and re-inserted. I also found some DV clips audio to be 32 kHz, I converted these to 48 kHz. And after that all was well.
I’m not sure this is the same problem that’s re-surfaced in FCP 7.0.1, but just a thought.
One issue in OMFs that we are seeing (was so in FCP 6 as well) is that exported OMFs do not have time code from the original BWFs used in FCP. Especially so when the FCP clips are actually merged clips. This is separate audio in a film (24@25 project).
So we’ve put this down as an unresolved issue, probably affecting only PAL film projects.
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Neil Sadwelkar
neilsadwelkar.blogspot.com
twitter: fcpguru
FCP Editor, Edit systems consultant
Mumbai India