Hi, I have a MY17 RR Sport and when I use the cruise control on a long trip it does not hold the speed when going downhill. I had it set at 110km and going downhill I looked at the speed and was doing 135km/hr. I have been told that this is normal with the RR and they don’t hold speed. Is this correct? I find this really strange as I previously had an X5 and a ML350 and they both held speed going downhill. TIA.