To aid debugging I've created a webpage form that submits the data to Musicbrainz automatically on open (occasionally you have to retry because of a Bad Gateway Error, assume this is problem with server), just do view source to see the parameters sent.

1. When seed with this basic release data http://www.jthink.net/jaikoz/scratch/addrelease1.html no label box is displayed and the Add Label button doesnt do anything.

2. Passing an invalid value from list causes stack trace, i.e http://www.jthink.net/jaikoz/scratch/addrelease2.html passes a country code of USA instead of US, if invalid value value Release Editor should just ignore it not give

Caught exception in MusicBrainz::Server::Controller::ReleaseEditor::Add->add "Can't call method "id" on an undefined value at /home/musicbrainz/musicbrainz-server/script/../lib/MusicBrainz/Server/Wizard/ReleaseEditor.pm line 764."

3. If try and send track names i.e http://www.jthink.net/jaikoz/scratch/addrelease3.html as well get stack trace
Caught exception in MusicBrainz::Server::Controller::ReleaseEditor::Add->add "Can't call method "id" on an undefined value at /home/musicbrainz/musicbrainz-server/script/../lib/MusicBrainz/Server/Wizard/ReleaseEditor.pm line 764."

4. There is artist_credit.names.n.name field to let you add an artist without having to have found the Musicbrainz Artist Id , but there is no equivalent field for adding a label by label name.

5. The documentation mention both medium.n.track.m.length and medium.n.track.m.duration not clear what value each option should take.