not sure if this helps you, but on my bike, i know that if it's on the center stand, and i don't even have it in gear and it's running, it'll slowly turn the chain and wheel. something about all that fluid in the case, and rotational energy, and fluid dynamics saying that it'll try to spin things. ;-)
if it bothers you, you could probably loosen the clutch up a bit more, and it may stop, but then you run the risk of having the clutch too loose. so long as stopping the rear wheel doesn't cause the bike to stall out, i think you're fine