it is a pretty serious flaw with a structural weight distribution having to do with some larger engines. The thrust/weight combination causes a stall scenario that was kept under control with the fly-by-wire system. But in some specific instances, that system couldn't be counted on and the pilot had to take control... thus some of the airlines that had less-trained pilots were at a disadvantage at controlling these situations, especially if they arise at a critical moment during takeoff and pilots aren't ready. But this was all pretty early conjecture and I can't recall a single source, or if I am somehow piecing this together. Guess we have to wait and see.