I have to admit, I had over two thousand hours in the Gazelle before I realised there was such a term as Fenestron Stall, I had never heard of it, and didn't know I didn't know.
I was sitting in the back of a Gazelle during a short flight on my QHI course when the HP very clumsily tried a lookout turn to the left. The strong wind caught the big tailfin and whipped us even faster to the left, his reaction was full-right pedal, and off we jollywell went. After about 3 revolutions, I thought the shaft had failed, I could see he had full right pedal applied and nothing was happening. He instinctively raised the collective to get away from the ground but this made things worse so he decided to land very heavily whilst in the spot turn.
On further investigation of the twisted Gazelle, there was nothing wrong with the anti-torque system. If you apply too much pitch to an aerofoil, eventually it will stall, he had applied the maximum possible pitch, very quickly, and I would say the fenestron had stalled.
The French TP's answer was to apply full left pedal to unstall then re-apply right pedal gently. I have no doubt that would work, but try doing it when you are spinning at 360 deg in 3 seconds and out of control with your ar$e biting the buttons off the seat cushion.
Call it what you like, I would say the fenestron had stalled.
Tam