At the moment the display of that section is broken:
http://ngs.musicbrainz.org/release/4db70ed2-95b8-4a87-a1de-60c66e2c909f > No URL relationships, section header is there
http://test.musicbrainz.org/release/419b6085-c8d0-45d5-9602-8ab349c56482 > No URL relationships, section header is hidden, looks really bad (imho). There's no distinction between the collections part and the external relationships part