Oh, I see. The corkscrews just don't work very well with the 2D code. I actually thought I had it working a little different while you were in the air to prevent things like this but I guess I changed it back for some reason.
As for the slopes thing- that's just how it works. Once you enter a slope, the ground normal threshold lowers until you're on the ground again. Until then, player movement is treated as if you were in the air. The idea is just go fast enough so that doesn't happen.