The old qrh said open the x-feed after an engine failure after confirming no leaks. This procedure worked well on the sims. Sims are a bunch of electronics which meant both sides were giving equal fuel pressures. The real pumps have slightly different output pressures. On the real aircraft with all wing pumps running & crossfeed open it is possible that the live engine may be just using all the fuel from either wing. The (new) qrh procedure of monitoring the fuel imbalance makes better sense as long as it is not forgotten. Funny how long it took airbus to change the procedure however.