[yokohama]

I've had that before too. Health and safety reasons. They don't want any fuel dripping over a hot engine and igniting while the rider is sitting on the bike. And if this were to happen, it's likely the rider would leap off, dropping the bike, fuel spilling out etc etc.
Not having a centre stand, I refill mine on the side stand, level the bike, rock and shake to settle the fuel and put more in if needed.