Tree House of Horror XII - S13-E1
Audio problem: In 'Wiz Kids,' when Edna asks Harry Potter if he is chewing gum, he replies "No ma'am, it's brimstone," however it's clear that a different line was originally intended. (00:15:25)
Tree House of Horror XII - S13-E1
Audio problem: In Reaper Madness; the scene where Homer destroys the Grim Reaper with a bowling ball, Bart is pinned on the wall by the Reaper's scythe. The scythe disappears and Bart says "Cool!" but his mouth just opens up and doesn't match the word.
Weekend at Burnsie's - S13-E16
Audio problem: There is an elaborate bass line right at the end of Phish's song; however, the bassist's fingers don't even move. There's no way he could play that line without moving his hand. (00:13:50)
Half-Decent Proposal - S13-E10
Audio problem: The lady singing at the prom doesn't move her lips when she sings, her mouth just stays open.
Audio problem: When Homer says "He sees a thousand times worse on that animal channel", his mouth is out of sync when he says "channel."
Hunka Hunka Burns in Love - S13-E4
Audio problem: When Marge says "New underpants?", she is mouthing "New boxers?"
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