Audio problem: When Matt Groening is putting boxes of comic books into the Comics Bongo Group truck, he says "I'm so rich" but his mouth isn't moving. (00:04:40)
Audio problem: When Homer says "I need change for a dollar. I also need a dollar", his mouth doesn't match what he's saying. (00:07:25)
Audio problem: When Marge says "Now that it's empty, who's going to buy their house? What if someone moves in with two Barts? Or four teenage Barts?" her mouth movements don't match most of her dialogue.
Answer: I'm not sure if this is the one you're thinking of, but an episode of "Ray Bradbury Theatre," called "A Sound of Thunder," dealt with a similar matter: a group of hunters travel back in time to hunt dinosaurs, only to find things have changed when they get back because someone stepped on a butterfly.
Xofer