Our electronic Speed controllers in our RC flying stuff cab be set to allow free spinning of the prop or a brake stop with throttle "off" . The prop brake comes in handy when trying to land a glider else the thing wants to fly for ever. This is a software set up.(gliders are about the only plane where I use it)
MTH....Hardware or software issue. I don't know but I'd say your stuck with it unless one of the tech guys can fix you up.