1 Ensure Options, Tags, Mpeg, Read, [X] ID3v2
2 Load an MP3 file having a ID3v2.3 text frame having post-terminator characters e.g. bbb
3 In the tag panel, inspect Artist
4.2. Text information frames
... If the textstring is followed by a termination
($00 (00)) all the following information
should be ignored and not be displayed.
This different interpretation of the specification is intended. There are two many files and programs out there, that treat the separator as in ID3v2.4 so if Mp3tag would do differently, there would be a lot more reports than those few which point to the misinterpretation of the spec.
I think it simply doesn't hurt to interpret it in this way.
I mark it as [X] where it means "Won't Fix" this time.