A few thoughts... Although Nebora only removes the one collar, you'll find someone else a bit later on who'll remove the others, at least once a condition is met.
I'm not sure that the trading button is a bug: I've used it quite often when there's no dialogue option is given to to see if anyone has anything interesting for sale (or wants to take some crap off my hands!)
I still haven't figured out the solution to the Rattus Perfidus conundrum: I think source was mentioned at one point so it could possibly reference a spell that isn't currently available to us, perhaps.
