That is called ‘comfort locking’ and has been a feature since at least the days of the W124 : hold the key in the ‘unlock’ position for three seconds and all windows plus sunroof will open ( very handy if you return to the car on a scorching hot day , and you want to ventilate the car before getting in ) , and likewise, closes everything if you hold key in lock position on exiting.I only found out this weekend that if you press to unlock and hold the unlock on the key it opens all the windows and rolls them up doing the same with lock and hold.