That is not a problem. That is what it is designed to do. The throttle hold function 'holds' the throttle at a set position and allows movement of the collective. It is usually set with the throttle at at high idle.

You can now practice autorotation at the flick of a switch. The throttle goes to idle and you still have control of collective. When you need the engine back you flick the switch back and it is now coupled again.