pie Chaser,
I have looked at the fuel diagram and If I read correctly, the pilot posters suggest that with a nose up attitude, the fore pump in the main tank may be isolated or it will run dry, using the aft pump only.
The suggestion is that the check valve on the fore pump was jammed open so the fuel was merely being pumped from the back to the front of the bulk storage tank.
although the diagram doesn't show the pipe sizes, I would still expect fuel to reach the individual engine tanks, as there is far less restriction here, the pipework is shorter and it doesn't need to overcome a check valve, which I still don't accept as being jammed fully open, although it may well have been passing.
I would also have expected the pipework supplying the 2 engine tanks to be equal, I.e self balancing and not the unequal tee arrangement shown, though I'm not from aviation though as you can probably tell from my terminology!
also, I believe this is a German designed machine, and they are known for engineering clumsiness rather than simple and elegant engineering solutions, so they may just run higher pressures and not bother with hydraulic balance, as the tanks overspill anyway, in normal and single failure modes, it does work.