In the episode "Traffic Jam", go to the part where Lois spots a dog locked inside a van. Nobody claims the dog is theres so she picks up a rock and smashes the window. Notice that there is still broken glass in the window around the edges, with quite a large piece at the bottom. The camera then switches to the outside of the car where we see that all of the glass is gone, as if the window has just been wound down. The camera then switches back to inside the car and again we see the broken shards around the edges. Once more, when dog jumps out of the car, the shards have disappeared again.