I saw earlier that the 'rotor brake' had been discounted in an earlier reply but can't find where that was mentioned in the thread. Is it as simple as the rotor brake being locked out in flight?
It also seems very close to the engine controls from the panel diagrams I saw and I wonder if trying to shut down an engine in an emergency situation could also have resulted in accidental application of the rotor brake. Removing power from a misbehaving engine and applying the rotor brake might explain everything observed from the ground.