it occurs in Berlin Tegel EDDT at Gate 4 (standard FSX Airport, no Scenery installed ) and there is an Jetway, but you can not move them.
If you cannot move it, it doesn't depend on GSX, this is explained in the manual and on the forum, many times, GSX doesn't change or control if jetways move or not.
Since at default airports, jetways are always "animated" (if the don't actually move, it's usually a placement problem or a parking radius problem), so they are flagged as jetways, and GSX will recognize them as such, preventing the stairs to appear.
Again, when you find such case of proper jetways that don't move, and you want the front stairs, the solution is the same: use the GSX editor to tell GSX there's NO jetway there, so front stairs will appear. Since these cases are fairly rare, it's of course better to configure them for a single parking spot.
Sometimes it occurs that you arrive at a Gate without a Jetway, but there comes no Stairs..
If it's a default airport, it's likely you don't "see" the jetway, because your Scenery Complexity level is not set at the highest, so you are not seeing all the jetways in the airport. Since the jetway is in the .BGL, GSX will of course not display the stairs, because it knows it's there, even if your scenery complexity level prevented to display it.
Of course, this is not a GSX problem either, and you can "fix" it either by raising your complexity level to display the jetway OR editing the parking with the GSX editor to tell there's no jetway there, but will have to remember that in case you'll eventually use that scenery at the highest complexity level, the jetway will reappear, and front stairs (and a Passenger Bus) will appear too, so you'll have to change it back.
IF you are suspecting a "problem" with GSX jetway recognition, before reporting it as a problem, ALWAYS check this first:
Open the GSX editor and see if GSX found a jetway there.
If GSX has the "has jetway" option enabled, and you see front stairs OR if GSX has the "has jetway" disabled and you DON'T see front stairs, then we have a problem, and you can report it as such. Otherwise, it's all behaving as expected.