i tested, everything seems to be ok.
i edited tags in winamp, id3v1 different from id3v2, Similarity showed correct id3v2 tags, in win2k,winxp.
can you send me this file where this bug appears ?
similarity don't analyse file for id3v2 tags, it uses Windows Media SDK for taking all information, maybe your grabber write invalid tags ?
Or you maybe didn't install Windows Media Player 9.0 or later, in this case Similarity uses ACM decoder and himself searches ID3v1 tags. In this mode it's not support ID3v2.x tags.