HID self-leveling

Hi Guys, I noticed only once that my car's factory HID headlights did the self leveling thingy when I parked my car at a slope and switch the headlights on at night. But, I have never seen it since, is it suppose to be obvious? I have seen other cars that does the self leveling thing everytime the headlights are switched on regardless of whether the car is level or not?