Continuity mistake: The bible that Reverend Lovejoy returns at the library is bigger in the first shot.
Continuity mistake: When Bart says "Everybody, come quick!", the fridge door goes from open to closed.
Continuity mistake: In this episode and maybe in other one, the door to the basement is at the entrance of the house, but that's a closet in other episode.
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