Hi Umberto,
I've just tested it again and it's definitely GSX clearing down the payload fields with the exception of the pilot field which remains at 180. Rather than attach the whole aircraft.cfg I'm pasting the payload and fuel sections for info.
max_number_of_stations = 9
station_load.0 = 180, 2.5, 0, 0
station_load.1 = 0, 2.5, 0, 0
station_load.2 = 0, 1.5, 0, 0
station_load.3 = 0, 1.5, 0, 0
station_load.4 = 0, 0.5, 0, 0
station_load.5 = 0, 0.5, 0, 0
station_load.6 = 0, -0.5, 0, 0
station_load.7 = 0, -0.5, 0, 0
station_load.8 = 0, -1.0, 0, 0
station_name.0 = "pilot"
station_name.1 = "pax fwd"
station_name.2 = "pax 2nd row"
station_name.3 = "Pax 2nd row"
station_name.4 = "pax 3rd row"
station_name.5 = "pax 3rd row"
station_name.6 = "pax 4th row"
station_name.7 = "pax 4th row"
station_name.8 = "400lbs max"
[fuel]
LeftMain = 0.5, -4, -2, 203, 2 //Longitudinal (feet), Lateral (feet), Vertical (feet), Usable(gallons), Unusable (gallons)
RightMain = 0.5, 4, -2, 203, 2 //Longitudinal (feet), Lateral (feet), Vertical (feet), Usable(gallons), Unusable (gallons)
fuel_type = 2 //Fuel type: 1 = Avgas, 2 = JetA
number_of_tank_selectors = 1
electric_pump=1
If you require any more info just ask.