Got my new to me 550i today. It seems to do something really weird.

When I stop, put it in park, then hit the start/stop button, it turns the engine off, but seems to leave the car in accessory mode, so if I get out of the car, the radio stays on. I have to push start/stop twice to get the car to actually turn off after I've put it in park before I get out to ensure the car is off.

What am I doing wrong