the code i use for making musicbrainz requests seems to ask for all "rels" (artist-rels+release-rels+track-rels+label-rels+url-rels) with release-group requests. this absolutely used to work. since the ngs release this behavior has changed. it now returns an error response:

artist-rels is not a valid inc parameter for the release-group resource.
For usage, please see: http://musicbrainz.org/development/mmd

nowhere in the documentation at that given url is information given about which rels are supported for which requests.

behavior has changed unnecessarily, without any positive effect and without warning. further, no documentation is available to aid in migrating to the new behavior. how are your users to proceed??