If a FLAC file has Vorbis tags and ID3v2 tags then %_tag% expands to "FLAC ID3v2".
Good. This shows me the files that should be edited to remove the ID3 tags.

However, without using Mp3tag, I accidentally discovered several FLAC files with ID3v1 tags. %_tag% expanded to "FLAC".
Therefore, there was no indication of the "improper" ID3 tags that I want to remove.
I could still remove the offending ID3v1 tags in the usual way but I only knew they were there by a lucky accident.

Does Mp3tag ignore ID3v1 tags in FLAC files?

It would be better to indicate any and all ID3 tags contained in FLAC files.