I have found a work around the fuel problem, After loading your aircraft set the fuel in the centre tank to zero this will cause the engines to stop, once stopped re-start the engines and they will run off the other tanks, once all engines are running you can go to the fuel/payload section and put your additional fuel in the centre tank, the engines now run on the centre tank but they now will continue to run even when the centre tank goes empty. I have tried this on the MD11, A380 and the B752 and it worked for all the aircraft.