I've had the same thing happen to me. Pulled into supermarket parking bay. A.S.S kicked in. Put it in P, got out and locked the car. The radio turned off when the car locked as usual. So I thought nothing of it.
I returned about 40 minutes later to find the engine running! I've not managed to replicate the fault, but normally the needle goes from ready to off as soon as you open the car door. Very strange.
Mine was delivered to me in early Feb so was probably one of the first in the UK.
320d luxury with sport automatic.