Speakling of disengaging the freewheel.
The only way I can get it to disengage is cutting the fuel. Rolling off the throttle (With or without the Governor switch on EMER), keeps the engine pegged to the RRPM.
Seems like a bug to me as I've seen it behave correctly in some of the older DCS Huey Auto videos.
It doesn't, however, appear to be influence the autorotative performance much.