I have electric planes that the prop windmills so much you would swear it must be pulling at zero throttle. I am betting its a efficient gliding plane that is slightly nose heavy as well.
Trixie had my hopes up that perpetual flight had finally been discovered.. but after awhile I figured we weren't breaking that law yet !
One thing OP could try is setting his motor up to SOFT BREAK, possibly that would slow it down a bit...though its my understanding that once the prop stops it would still cause very little drag...