Sorry thought you had this:
I guess I missed that. I tried the direct m4a link and it wasn't working.
Does this only happen when the buffering of the mp3 starts (I don't think the first file will fit in its entirety)? I ask because I don't know if I'll be able to duplicate it because the closest device I have as far as memory size is a Fuze V2. My only AMS V1 is a clip with only 2MB.
I'm suspicious that it's low-level if it's specific to certain devices. It's worth mentioning here again that the newer file system code doesn't align buffers at the file API level, which already had side effects on another model but that was fixed up.
It's also possible that obeying POSIX more closely actually changed some expected return values/errnums.
Getting a sentinel-marked buffer dump would help me see if the last handle for the MP3 metadata isn't just being clobbered on account of over reading the previous M4A.
Well, I've got plenty of ideas of things to check but not much info yet to start ruling things out. Will get back...