I tried it now, and it doesn't happen. This is what I did:
- Went to an airport in which I replaced default jetways with GSX jetways ( I assumed this is what you mean with "I have a Position with a Jetway. IN GSX" ), in this case it was Simwings LEMD, Gate 71
- Select "Disable Staircase" in the parking customization page. Pressed Apply.
- Selected Deboarding. Jetway menu came, docked to Exit 1, no rear stairs appeared and the only door request I got was for the main Exit 1, as expected
- While passengers were still exiting, I chose "Reset Position"
- Selected Deboarding again. Jetway menu came, docked to Exit 1, no rear stairs appeared and the only door request I got was for the main Exit 1, as expected