For MP3 files (i.e. ID3 tags), MP3Tag only writes one Artist tag, with both names contained within the same field, as the spec does not allow for two separate instances of the same tag type. For FLAC and some other formats that use Vorbis tagging, MP3Tag converts any Artist tag which contains "\\" into two separate instances of the ARTIST tag, one for each split name, which is permitted in the Vorbis spec (but not in ID3). So for MP3 files you should see both names in PA, but for FLAC Power