I bought a new BMW 420D Gran Coupe seven months with active cruise control. The system detects the car in front and maintains a safe distance, would I thought be a useful safety feature. However, since driving the car, I've noticed that it does not detect stationary cars. For example at traffic lights or a tailback on the motorway. This is dangerous in my view.

BMW say that there is nothing wrong with system and if I wanted the 'stationary' feature I need to have an additional technology pack, but my local BMW dealer in Sheffield was not aware of this. How BMW can design a radar based system which does not detect stationary cars?