Release and recording pages should include links back to the entity pages for the instruments used on them.

For example: http://musicbrainz.org/release/a057fffa-6c96-467b-9c08-6563c56350f6 should have a link to http://musicbrainz.org/instrument/9cbe04a2-0014-474c-b530-b0d4f4b73413/releases

and

http://musicbrainz.org/recording/db4dbe87-a038-43e1-a231-db4d75e7b83d should link to http://musicbrainz.org/instrument/9cbe04a2-0014-474c-b530-b0d4f4b73413/recordings