Work around that works for me (PMDG and A310) - until Umberto believes us, that there is something wrong:
1. Keep the doors shut before starting GSX - no stairs, nothing.
2. Prepare the plane (GPU, IRS, FMS, etc.). Set you parking brakes, even if you're still on chocks (PMDG).
3. Request fueling
4. Wait until this is done and the fuel truck left the aircraft
5. then you can call stairs, open doors, call catering, etc.