Audio problem: When Otto says that he was on his way to Mexico, his mouth doesn't move in the interior shot of the bus. (00:04:20)
Mr. Lisa Goes to Washington - S3-E2
Audio problem: When Lisa is reading her speech for the essay contest, what she says does not match her mouth movements. (00:06:30)
Tree House of Horror II: A Simpsons Halloween - S3-E7
Audio problem: When Kang and Kodos land in Springfield and hit Mayor Quimby with a club, one of them says something but his mouth is not moving.
Audio problem: When Homer pulls Lurleen away from her trailer, she says "Ooh" but her lips don't move. (00:09:20)
Audio problem: When Homer sulks about not knowing anything about Bart, his first words of speech doesn't match his mouth. (00:08:20)
Audio problem: When Michael and Bart are playing a song to Lisa, Bart uses her bin as a drum. Sometimes you hear tapping, but Bart doesn't touch the bin.
Audio problem: When the old lady is playing the keyboard at Homer and Marge's wedding, her hands don't match the music.
Homer Alone - S3-E15
Audio problem: At the start in the kitchen when Homer, Bart and Lisa are all talking over each other, their mouths don't match what they're saying. (00:02:30)
Audio problem: When Moe says "I'll talk to you tomorrow" to Homer, his mouth doesn't move. (00:15:15)
Audio problem: When Krusty arrives at the bar, Bernard says "Hey Krusty" but his mouth doesn't move. (00:11:00)
Audio problem: When Ned calls Homer and says "over here" his mouth doesn't move. (00:17:30)
Audio problem: When Bart says "I'm going to find my dog" his mouth does not match what he is saying.
Brother Can You Spare Two Dimes? - S3-E24
Audio problem: When Lisa says "I stand corrected" at the award ceremony, her mouth doesn't match what she is saying. (00:07:25)
Tree House of Horror II: A Simpsons Halloween - S3-E7
Audio problem: When the guy who Homer buys the monkey's paw from tells him that he'll be sorry, his mouth doesn't move. (00:03:10)
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