Darth Editous said:

Remuxing to a .mkv without reencoding the audio should work in this case.

I didn't have to reencode either the audio or the video from my problematic .m2ts - I just had to put them both in a .mkv container and all was fixed.

Wait a minute. I agree that re-encoding is not necessary if LG is simply changing containers, but if he has changed the frame rate from 24 to 23.976 fps, surely it is necessary. I had to do this when I re-encoded the AVCHD of EP.IV to make it work properly.