Post #237 (Svarin) and post #260 (mm43) are both recommended reading.
Re #237 : Svarin's speculation has a certain uncomfortable ring of truth. Protection mechanisms can be a doubled edged, and can often bite when one of those 'unknown unknowns' comes out of the woodwork. Post #4 in "Not good in an ETOPS/EROPS TWIN" is an excellent description of a similar conflict between man and machine.
http://www.pprune.org/tech-log/43214...rops-twin.html
It falls under the general category of "deadly embrace," where neither of the two control entities has both the information and the ability to resolve the problem.