the Hurth has a multi disk clutch pack which is loaded by ramps in such a way that they will release pressure on the packs on over run. So if it freewheels in reverse, the shaft is running in reverse.

Thinking about it for a second (always dangerous), what you say must in fact be correct. The way the Autoprop works is the blade is offset from the pivot point such that the lift forces cause the blade to rotate into pitch at the correct angle. With the shaft stopped under the influence of flow parallel to the shaft, these same forces will cause the blade to go into a very high reverse pitch. Essentially, from the prop blade point of view, the apparent flow has changed from almost athwartships (while being driven by the engine) to ahead (when stopped), and the prop angle relative to the boat has to change from slightly forward of abeam to slightly off the opposite bow - reversing its pitch.

So with the Autoprop you would need to put the transmission in forward to stop it. With any other prop, reverse.