I have another idea.
I noticed looking at the drawings supplied by Machaca, that all 3 fuel pickups are located next to what appears to be a bulkhead between the main tank and the center wing tank. Since the center wing tank was basically empty at this point in the flight, what would the temperature of this tank have been? If this empty tank was colder than the fuel in the main tank, how would this have effected the portion of fuel in the main tank located right next to the bulkhead (where the fuel pickups are)?