The switch to clipless caused me significant pain for the first few days. There was definitely different happening. It was a change, but I think it was a good one as I've had no significant knee discomfort since I did the switch, over a couple years now. It's like if you sit on your foot it will hurt briefly when the circulation comes back, but it's a good thing. I think it was a similar thing, where I was getting a fuller and more comfortable range of motion from having a little float.