I initially had the same problem with my velocity 1's (and apparently it was common with the first generation velos...based on the archive here)
I did three things.
1. As Huntster suggested, I tightened the top calf strap a bit.
2. I cover the gussets of the pads with duct tape (white to match the pads...you cannot tell at all) so the pad doesn't stick to the floor.
3. I got bigger knee blocks from PAW.
