A Totally Fun Thing Bart Will Never Do Again - S23-E19
Audio problem: While Bart is in the communication center, the second time Bart says "Squirt!", his lips don't move.
The Man in the Blue Flannel Pants - S23-E7
Audio problem: When the woman on the DVD Bart is watching says "Are you sure you're Martin Scorsese?" her mouth is completely out-of-sync with her voice.
The Man in the Blue Flannel Pants - S23-E7
Audio problem: In the rafting scene, while Marge says "And maybe when we get home, we can ride down something else?" part of her dialogue does not match her mouth movements.
Audio problem: When Homer, Bart and Lisa enter E4, when Homer says "Wow", his mouth doesn't move.
Bart Stops to Smell the Roosevelts - S23-E2
Audio problem: During Superintendent Chalmers' flashback, when he says "So, you are the so-called Breakfast Club?", his mouth movements don't match his voice.
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