I have experienced it in both single player and online.
When you enter walk mode and stand idle your character will twitch jump up and down.
I play on European servers but I have talked with Americans who experience the same bug
When you walk and enter third person you can see the character twitching up and down.
You press the walk key and scroll out the camera to third person view and then you can see the character jumping up and down slightly. It is the same problem for all and everyone I have talked with.