I notice that if I search my library using ['songs', 0, 500, 'search:' + what, 'tags:Aal'] where what is a single word like Chicane, the search results only match in the title tag. So songs such as 'She's Got a Way (Chicane Mix)' will match because the artist Chicane is mentioned in the title tag.

However, if what consists of more than one word (e.g. Bob Seger, Armin van Buuren, Everything but the Girl) then the search matches in the artist tag also and I can successfully use it to peruse all tracks by that artist.
I know I can use artist_id with the API but the problem is that collaborations result in extra artist_ids for an artist in combination with somebody else. The artist_id for the bare artist will miss those tracks.

The Full Text Search plugin is enabled. This behavious eems to be version independent because I also had this back on 7.9.2 but FWIW I'm on the latest debian nightly.

Is this a bug or am I somehow misusing the songs query?