I think the creep function is somehow involved.

I have a 450 as well which does not do any of this. In the 451, when I slow down for a stop light without braking, the creep function kicks in with a thunk, then I do have to brake to stop, rather than just coasting in. Also I have a very steep downhill to the garage entrance and I turn him around to back into the garage(very tight turns). Smartie just seems to get all rev'ed up from the descent so when I make the turn around, he lurches forward in 1st and backwards in reverse. I just let him roll backwards into the garage in N, rather than fighting with reverse. Hope he calms down soon. (200 miles on odo)
If there were one mod I would do, it would be to cut the creep function. I'm hoping eventually someone comes up with a way to disable it. Seems useless to me. IMHO