I made a right pig's ear of http://musicbrainz.org/release/4fa785a2-f7c2-4883-bf6d-95b1278971fa

What actually happened - I spent a long time in the RE improving the relationships. I submitted my edits and got an error - I'm really sorry I didn't copy the actual message, but it was of the "too much data" variety. So I backed out most of my changes and tried again a few times until it was "small" enough to slip through.

What I didn't know was that parts of of my failed edits were accepted, so I ended up with multiple identical Recording-Work ARs.

So quite a few issues here - a problem with the transparency and robustness of the RE, but most significantly the RE can enter duplicate ARs.