Hi. Try turning off the climate control fan, by pressing the ON/OFF button, so that it doesn't blow any air into the cabin. Then see if the engine stops, when you stop the car.
In cold weather the engine may keep running, even when the car is not moving, because it's trying to heat up the cold cabin air. It produces the heat by idling the engine.
In summer, the engine should stop almost always when you stop the car, unless the HV battery has less than 3 bars of juice left, in which case the engine would run to charge the battery.