I've landed in Stendal 3 or 4 times in a 44 to refuel. Massive ex Soviet Air Force Airfield, you land right next to the fuel bowser, next to the tanks, 10.000 Liters each I think. How you can NOT read the type of fuel IN THE BOWSER window, next to the ammount in liters, I have absolutely no clue. It also says the type of fuel (JetA1, Avgas 100 LL) on the big tanks on the side and front. And those guys usually fly with 2 pilots and at least 1 observer/ crew so 3 pairs of eyes who didn's see they were refueling the wrong type of fuel
TWICE
The fact that it happend at night isn't really an excuse....