Pumpers Puzzle

Ok, so I have a conundrum and have put it to our company veterans and even our trailer mechanic. This was a diesel pump load. I had 3000 in the first compartment, 1000 in the third, 1000 in the fourth and 2500 red in the fifth. I pumped #1 off, then 3, then 4, switched tanks w/o moving the truck, then pumped off 5. I used my PTO driven suction pump. Never turned it off. I switched compartments the way I always do by waiting for the open empty compartment to allow neutral pressure for me to remove the hose slightly by hand then close the compartment, pull the hose all the way off, and move to the next one. Yet, somehow there was 200 gals left in 3 and 700 gals left in 4. If it were an air issue then the belly valves all shut and stay shut and if that hose is on there the pump sucks it on where you would not be able to remove it by hand. How did I do if and not get fuel everywhere? Didn't even seem like anything was wrong. Explain that.