Update:

I went to the airport first thing this morning to turn the prop with the
engine cold. As before, I felt good compression at each cylinder, and the
prop stopped at 02:30/04:30.

So I ran the engine for 3-4 minutes, just to get the oil a little warm, and
shut it down. Voila': the prop stopped at its usual 09:00/03:00 position.

I don't know WTF to think, now.

Wait a minute, yes I do: I think I'll have a couple of Coronas and forget
about it..

--
Dan
C-172RG at BFM