If I’m doing something wrong, I can’t see what. Is this a bug? Or does “guess case” use a rule I’m not aware of? Or maybe it’s just working that way for me? Can anyone else reproduce this behavior?
It’s because the text in parentheses is detected as Extra Title Information, and there apply different rules. See the comment at Style / Language / English - MusicBrainz
Yes, “with” is always capitalized, unless it’s ETI. Guess case assumes it’s ETI like “with such & such artist”, which I always found weird because we aren’t supposed to have artist in the ETI. So, it should be fixed to always capitalize with.