I obviously haven't driven your car but in mine, after 7,000 miles, I have never experienced the car braking of it's own accord, other than when using ACC (whether in response to proximity, a change in speed by me or a change in speed limit) or one time when I was slowly reversing out onto a road and a it spotted a car coming and slammed on quicker than I could brake.
The only thing that I can attribute to what you're saying is the difference in how the car feels when coasting (essentially in neutral) and when coasting switches off and the car goes back 'in gear' - ie; engine braking.
The car will switch off coasting when it comes into close proximity to a car in front resulting in engine braking being felt. This can normally be seen with it's own symbol showing that you're too close. It also turns off coasting when going too far over the speed limit, again resulting in engine braking being a factor. It is possible that the car will also switch coasting off if there is an impending corner - often shown when the car tells you to lift of the accelerator. However, I am pretty sure that the car does not engage the brakes in any of these situations and it is only the car being put back 'into gear' that makes the car slow down.
Again, without driving your car I could never know for sure but, if you're reading this and thinking 'I know what engine braking is and this is different', then I would take the car to a dealer to be looked at.