Sorry guys as I don't have any Boeing manuals here at the moment but I believe it has to do with a C system hyd failure and the fact that the AP will remain engaged in spite of this event. Maybe someone can jump in here a refresh my memory regarding how this works. Also, one needs to be cautious when discussing AP on the various 757/767 as there are several configurations out there and the one your operating with may not use the same logic as the next guys.