This drives me nuts too.... lets take the A3XX pro for example... as soon as I hit the load fuel button, the fuel starts to flow long before the truck arrives, and I wait ages for the truck to complete, even though the aircraft already has the fuel I requested via the load-sheet. Also noticed, that if you put the APU on prior to boarding - which I often do - I fly in and out of Middle east countries, if the APU uses some of that fuel, the truck comes back again.
A dismiss or disconnect or manual fueling completed option would be great.