The Artists tag is incorrectly set on Album objects when Artists only applies to Tracks.

In mbxml.py in artist_credit_to_metadata:

166: m["artists"] = artists
167: if release:
171: else:

Line 166 should be inside the else clause (e.g. after line 174).

This issue has been addressed by PR-268 https://github.com/musicbrainz/picard/pull/268.