If the system disconnects autopilot because it senses that it has a fault, why isn't that fault also the basis on which its ability to command the aircraft contrary to the manual commands of the crew also disabled - that is just a fundamental logic flaw in the programming which ought to have been picked up in avionics testing.
I hope the public (and media) realise that this vindicates Qantas and that the skilled actions of the crew in the face of the erroneous stall and overspeed warnings, etc they were getting from the faulty avionics was really first rate.