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On my O-2, I feathered each engine in flight (one at a time) and performed a complete shutdown, ie, mixture to idle cut off, mag switches off,etc. When the front was shut down, I hand pumped the gear down to make sure that everything worked as planned under a controlled condition, before it was an emergency condition. I then unfeathered each engine and did an air restart, no problems. The O-2's have unfeathering accumulators, so that made things go a bit faster.
I'm not sure what damage you can do to an engine by feathering the props fully, in a normally aspirated engine? The only thing that I can possibly see is that it puts additional stress on the starter and starter adapter because of the aerodynamic load.
I've been bending wrenches on airplanes since 1975 for a living, and there are a lot of wives tales, half truths and superstitions among all types of A&P's/IA's. When I see something from a manufacturer that says its OK to do, or directed to do, as in a checklist, there has been some discussion from the engineers that this is an approved proceedure.
The internal feather latches on the prop blades are inhibited below approx 1000 rpm so its not necessary to go below 1200 rpm to check for feather and I think that the governor won't govern below 1500/1600 rpm unless the pilot spool/control arm is out of rig. The latches keep the blades from going to feather below 1000 revs, as a normal shutdown. I had a prop that would go to feather during a normal shutdown, and the latches were sticking retracted, allowing the blades to go to feather due to spring tension.
Cycling the prop only once will not purge the cold oil out of the dome, but it may puge any air that may have accumulated there during a shutdown period. It doesn't take a large volume of oil to change the pitch.
What everything boils down to is that TCM is going to have to issue a service bulletin that says feathering a prop will damage an engine before I beleive whats being tossed about.
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