Mp3tag not reading both id3v1 and id3v2 tags in some files

The problem in this file is that after the last valid frame TSIZ there's this:
MP3ext MP3ext MP3ext MP3ext MP3ext MP3ext MP3ext MP3ext MP3ext MP3ext
Which is not valid, it should be all zero bytes instead.

You can fix it with the hex editor or try changing a tag with another program, maybe it corrects it.
Maybe Florian wants to do a workaround.