I think you are mixing up the ZF25M transmission and the ZF25. The document you reference is for a ZF25M, not the ZF25. This has been a common source of confusion on the forum, since both of these are the common transmissions used in many Amel boats. The similar model numbers for two very different machines has always been an issue.
This is my understanding of this un-necessarily complicated issue:
The ZF25M is a smaller, lower horsepower rated, transmission that shifts mechanically. I believe none of these transmissions were ever fitted with a shaft brake, because none was needed. The ZF25, even though it has a very similar part number, is a very different beast. I doubt the ZF25M and the ZF25 have any parts in common. The ZF25 is a higher horsepower rated, hydraulically shifted, transmission. As far as I know (and this might not be correct) the Volvo TMD22 engines all had ZF25M and the Yanmars all had ZF25. Note that these model numbers changed when the original Hurth brand was bought out by ZF.
As the document you quoted points out, the ZF25M can free-wheel without damage, other than routine wear on bearings and seals. With a normal fixed prop or a MaxProp, putting it in reverse will lock the rotation. The AutoProp is a different story. It rotates in the opposite direction when free-wheeling, and needs to be put in FORWARD to lock it. The rule for operation should be “Do not allow the transmission to free wheel while in gear—ever.” If the prop rotates while in reverse, put it in forward. And the other way round.
The ZF25 relies on the hydraulic pressure generated by the rotating input shaft (from the engine) to shift. If the engine is not turning, it will always be in neutral, and neither forward nor reverse can be engaged no matter what the position of the shift lever. Therefore, the prop will always spin when the engine is not running. Most hydraulic transmissions require the engine input shaft to be turning to pump the fluid internally to lubricate the moving parts. The ZF25, however, is allowed to rotate with the engine off. It will be noisy, and add routine wear to the bearings and seals. There is no way to stop the rotation without a shaft brake.
Here are the rules:
If you have a Volvo with a ZF25M transmission:
The boat is in Charleston, we are in Antigua finishing up a delivery.