I'm thinking that somewhere along the line, the files are changing ever so slightly and corrupting. I've shrunken my experimentation down to a handful of albums of mixed functionality. I'm running some tests on them with different encoders to see if perhaps that makes a difference. They're all mp3. I check the tag file generated by mp3tofid and even the dead files have "codec=mp3" in them. I'm stumped.

Tony, I'll compare the two files to see if something changes somehow.