When lookup release & inc=tags+artists+artist-credits shoudn't show tags for artists within artist-credits within recordings because if listing recordings for a release likely to have the same artist for each recording and artist tags can be quite long ending up with alot of duplication of data, compare

http://test.musicbrainz.org/ws/2/release/2017f67b-02f2-4f04-9d09-2d877018567b?inc=recordings+artist-credits+release-groups+tags

with

http://test.musicbrainz.org/ws/2/release/2017f67b-02f2-4f04-9d09-2d877018567b?inc=recordings+artist-credits+release-groups+artists+tags

and see discussion
http://chatlogs.musicbrainz.org/musicbrainz-devel/2011/2011-05/2011-05-10.html#T17:59:23