A friend of mine has uploaded two albums, when I tried to modify the tags of the m4a-files I noticed that always the track number 10 and 20 were corrupted. I could play them with Winamp, but after modifying the MP4-Tag there, the file couldn't get played anymore. With Mp3tag (mp3tag.de), I couldn't modify the tag: File couldn't be opened in order to write.
Didn't test it with mp3, but maybe HFS stops the last file too soon when uploading 10 files at once?