No, he's always been fine having his tail messed with, and he doesn't clamp it when you lift it. He's never spun around on the lunge line and gotten the rope under his tail.
It was my first lesson with her and she just explained it as "He needs to have it under his tail". He was good when she lunged him with it, but now that you mention it I find it weird that this was my first lesson with her. No riding, No horse care advice, just putting my horse in her round pen and cantering him around with the rope under his tail. It was my first time out at her barn too. I'm questioning whether or not I should go back, it was almost like she wanted to test a new exercise on my horse before she attempted it with her own.