Sid,
I experienced an engine failure in a Hughes 500D many years ago. I got the aircraft down safely....not a mark on it....and upon landing I would still swear I did not see all five blades pass by the nose before the Blades came to a jerky halt. The Autorotative RPM seemed fine....but the first indications of an engine failure were a bit confusing as it appeared the engine was putting out some power until I raised the Collective a touch and then it started getting ugly quick. Luckily I was way too high for such things.....about 9,000 feet AGL just coming of a Mountain Top in Alaska.
Tear down of the Engine later determined a bearing failure that allowed the power turbine to bind up against Gas Producer shaft....or some such thing.
In my event, turning the Rotor Blades also turned the engine....which was more than a bit interesting to listen to.
The AAIB made no mention of anything like that in the Glasgow Crash and until we hear from them in some sort of Report.....we do not know for sure there was no mechanical defect that played a role in the Rotor Blades coming to a stop very quickly.