i have had that problem a few times. now i'm very careful to make sure that my heel is all the way back. i think that since the highback is very curved at the bottom it tricks me into thinking my heel is all the way back, when really it isn't.
Yea, I'm hoping thats all it was. It was late in the day so I just figured my turns were sloppier because I was getting tired. Didn't even notice it til I got to the lift.