Apologise for thread drift. Good points Beez 51. It was not common but no overtly rare that on shutdown in the PC9 that the prop did not feather due to misalignment of the S86 or may have been S82 (long time ago) micro. You than could sit there and watch as the prop slowly move to feather. If memory serves, up to one minute. And as you stated whilst gilding at 120kts, with air flow through the engine, and the micro connection failing, there was a lot of speculation of as to whether the prop would feather with oil px still provided. Many discussions on what to do including a stall turn, but if you couldn’t hang for more than a minute not going to work.
On the comment of the engine failing and the prop not feathering with air flow through the engine, once the S86/82 micro is made (hopefully aligned correctly) that opens a valve in the CSU that dumps the oil (return to engine) so no oil/px to stop the spring from working.