At first I thought the grass flying up in the sky and then flying up at a different spot is indicating that a Pokemon has moved around.
But when I walked past the Pokemon twice, they appear at the same spot, and another cellphone and account show the same location too. So do Pokemons not move at all? If so, then what does a lure do, if it won't move the Pokemons over... does it "move" the newly spawned Pokemons closer to the lure?