Had my new 2.0TFSI for just over a week. Coming down a very long gentle decent in Efficiency mode the car freewheels/coasts along then to my surprise at around 50mph the stop/start cuts in so the engine stops and the green A symbol shows. Tacho drops to READY position. Car steers ok so I'm still in control. Is it meant to do this or is it a fault? It's now done it at least 4 times!