Ed, sounds like you are going at it the right way. Now, if it only happens with rotors turning and not with the ground test rig, i think you are starting to narrow your problem down. What is in the system that operates differently with the test rig as compared to rotors turning? Im going to have to go back and check my 212/412 stuff, but is there not some sort of 3 way valve in the system, or a check valve that prevents ground test rig from driving the pumps/rotor system?
Also, as was asked before............with collective at flat pitch and engines at idle, what happens to collective when RPM increases to 100%? Does collective "jump up"?