GSX never opens any doors automatically so, either it's a feature of an airplane, or some other addon you have installed is doing this.
Also, GSX never changes the way you open doors. It doesn't touch any of the airplane systems so, anything you change in the GSX airplane configuration, won't affect how an airplane works in any way, it's only used to inform GSX of the actual location of the doors and the variables that controls the doors, but GSX *never* changes such variables, it only read them in order to know if it's a door is open or not.