I believe the car has some type of hill-stop function to prevent it from rolling back when in autostop.

I know it works, because I tried it the other day on a steep hill and when I let go of the brake... the car did not roll backwards.

HOWEVER... I can recall another instance (in traffic) where the car DID roll back during an autostop, as I was lifting my foot off the brake to begin accelerating. I had to abort the accel, and jam on the brake so I didn't roll back into the car behind me. I then used the handbrake while I was moving my foot to the gas. So... I guess it's intermittant! Be careful!