As explained many times already, GSX doesn't have any relationship with the jetways. What makes the jetway going to a door or another, is ONLY the Exit section in the aircraft.cfg.
Since FSX doesn't allow the jetway to go to the any other door than the main one, an airplane developer wanting to configure the jetway to go to what is *visually* the 2nd door, he will have to flag it as the 1st main door in the aircraft.cfg, so GSX will treat it as Exit 1, because it IS the Exit 1 ( main door ) from the FSX point of view.
So, what you are reporting is normal.