Surely some Whirlwind experienced Pilots had some exposure to that.
Yes. Almost 45 years ago, when I was a basic rotary student, my RAF QHI decided to carry out a “spirited arrival” at the unmanned Chetwynd airfield in Shropshire, first thing one fine morning. He descended to very low level at what was very close to Vne (not fast in a Whirlwind 10) and pulled the aircraft round in a hard turn. All I remember is being at close to 90 degrees to the ground, the aircraft wobbling slightly, then us being suddenly placed straight and level at a much reduced speed, alongside some 100’ high cables near the airfield. I was shaken rather than scared (the innocence of youth) but more intrigued to know how he’d done it. There was a nervous laugh from the other seat and he explained we’d just inadvertently experienced retreating blade stall. The aircraft did it, rather than himself.
So, very similar to the situation under discussion, although as far as I know, the Whirlwind reached RBS rather than jack stall/servo transparency, whatever we’d prefer to call it. It makes little difference to the symptoms. Had we been in a left turn, the aircraft might have put us inverted and I might not be here.
Sadly, said QHI was killed in a terrible motorcycle accident a short while afterwards whilst travelling on RAF duty.