In all fairness, some reported it came on unexpectedly. One described waiting at an intersection, started to drive and had to make an abrupt stop. According to them, HSA engaged as they attempted to resume driving. Perhaps the hard stop upset the sensor that indicates the car is on a grade? A surprise like that would be unnerving if you are sitting in the middle of an intersection.
Next time out I will drive a little harsher and see if it behaves any differently. It may be a few days, so if anyone else cares to try this feel free to chime in.