The fuel tanks NEED a slightly positive air pressure to help stop the tank collapsing when fuel is being pumped out of the tanks. The vent system provides this positive pressure.
I don't see how a jettison system can positively pressurise/aerate the fuel in the tanks. The wing nozzles face aft (no scooping effect)
How about the opposite of positive pressure in the tanks? With full fuel in the wings, maybe the float valves in the vent system iced up in the closed position (condensation + cold on the hinges and seals). Float valves have been know to stick before (but usually you only notice it when they stick open... dumping fuel in the surge tank).
Maybe the fuel being pumped out of the tanks to the engines gradually created a partial vacuum, and the fuel could not be fed to the engines fast enough at high thrust settings... hence the cavitation.
Looking at the diagrams in my manuals, it looks like all three tanks are kept at the same pressure.
Maybe just as crazy as the other theories, but I've been told it can cause problems in car fuel tanks
Looking forward to being shot down
(I've probably overlooked a negative pressure relief valve in the system)
Regards
NSEU