Either you or whoever made a GSX profile for that airplane must have disabled the "Show FSX Fuel and Cargo dialog during refueling" option, which by default is enabled.
When this option is disabled, you are telling GSX that airplane has a custom fuel loading panel ( either from a separate app or from its FMC, for example ) so GSX won't try to refuel the airplane by itself, but rather wait for you to act on that custom refueling method, and will only show fuel animations, without *actually* refilling the plane.
By default the option is enabled, and it should stay that way for most airplanes that use standard fuel systems. Basically, every plane the developer said it's safe to refuel using the standard fuel panel or the sim.
