The MP4 you sent me is a corrupt file. There is junk after one of the tag atoms.
iTunes can't read the tags, but does allow playback.
Is it possible you tagged the file with a third-party tool that didn't do a good job?
I'm going to try to update our MP4 parser to be more forgiving of tag corruption like this. However, the MP4 format doesn't really lend itself to sloppy data editing since it uses lots of exact byte sizes that reference other parts of the file in the header. Stream-type formats like MP3 are more forgiving since junk just gets ignored by the decoder.