Falling Damage
I have seen this as well. I fall, land, try to move anf the fall repeats itself, sometimes 3 repeats in a row.
It happens if you do -anything- in the air, usually when a skill doesn’t complete an animation. The easiest way to test is to interrupt a skill mid-air by swapping weapons, then swap back quickly.
Here’s a video of it: http://www.youtube.com/watch?v=xbD8PDHSOWc
It’s a real problem, it’s not lag related, and it’s connected to the bugs we’ve had since May began (basically, the game doesn’t know you’re on the ground after jumping, until you start running).