BPF,
Great post.
SSD,
The same thing happened to me, on instruments in a Chipmunk, west of Shawbury. Full power, 70 kts, climbing attitude and we were going down at 200' per minute. My instructor was laughing his socks off - he knew what was happening.
We were about 15 nm downwind of the beginning of the Welsh hills, but there was a weak wave, with completely laminar flow.