Continuity mistake: When Burns first shows the team the nerve tonic, the "&" on the 'Brain & Nerve Tonic' label is facing backward, but as Burns pulls it away it faces forward. Then as he moves it around as he's talking, the "&" switches between facing forward and facing backward again. This happens all in the one shot.
Audio problem: When we see Steve Sax driving, he says "What a nice little town" but his lips don't move.
Other mistake: In the end credits where it says, "Special Guest Voice", Marcia Wallace's name is there. Mrs. Krabappel was originally supposed to be in the episode but wasn't because Jose Canseco disliked his original part. He was originally slated to wake up in bed with her and miss the game, but Canseco's then-wife, Esther Haddad, objected. (00:29:00)
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