Don't Fear The Roofer - S16-E16
Audio problem: When Marge says "You're drooling on my goodwill pile", her mouth doesn't match her voice.
Catch 'em If You Can - S15-E18
Continuity mistake: When Lisa says "It's called Wicca, and it's empowering" to Bart, her necklace is red instead of white.
A Star is Born-Again - S14-E13
Audio problem: When Homer tells Ned "Flanders, I'm always interested in talking about free milk. And if there's cookies involved, so much the better", his mouth is not in sync with his voice.
Strong Arms of the Ma - S14-E9
Audio problem: When the woman who smashes the piano says "support the arts", her mouth is open, but it doesn't move.
Little Girl in the Big Ten - S13-E20
Other mistake: Sherri and Terri are seen participating in the second grade gymnastics (as referred by the gym teacher), even though they're in the fourth grade.
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.
Continuity mistake: When Duffman says "Duffman can never die, only the actors who play him", his red briefs are missing.
Sweets and Sour Marge - S13-E8
Continuity mistake: When Homer dumps the sugar into the ocean, the hand pressing the "dump cargo" button has a yellow shirt cuff. Homer is wearing a white short-sleeved shirt.
Sweets and Sour Marge - S13-E8
Continuity mistake: At court, when Garth Motherloving tells Judge Snyder "I'll kill you while you sleep", the blue haired lawyer's suit is green. His suit is grey in all other shots of him.
Continuity mistake: When Lisa comes and starts giving out apples, Moe is seen taking one of them, but some seconds later, he is seen under Homer's coat with a piece of Homer on a fork.
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."
I'm Goin' to Praiseland - S12-E19
Continuity mistake: Helen Lovejoy suddenly has lipstick on when she gives Homer the ice cream. She doesn't have lipstick on in previous shots.
Continuity mistake: Lenny's mug refills itself when he tells Homer, "You want to help me?"
New Kids on the Blecch - S12-E14
Audio problem: When the VJ on the TV says "That was the latest ad from Stridex pads. Medicated", her mouth is terribly out of sync with her voice.
Revealing mistake: When Lisa wraps herself in Marge's arms right before she falls asleep, the inside of her mouth turns yellow.
Continuity mistake: After Amy Tan shames Lisa, there is a shot of Lisa wearing a red necklace, her necklace becomes her usual white one, seconds later.
Kill the Alligator and Run - S11-E19
Continuity mistake: The 2 guitarists in Kid Rock's band swap hair color when Kid Rock first arrives on stage.
Audio problem: Superintendent Chalmers' mouth doesn't move when he says "Idiot."
Audio problem: When Homer says "According to my driver's license, I weigh 140 pounds" his mouth is not in sync with his voice.
Continuity mistake: After Lisa wakes from her daydream, there's a boy behind her with blonde hair and a light purple shirt. After Ms. Hoover says "Then come back and finish the test", the boy's hair turns blue, and after it zooms in on Lisa's face, there's a boy with brown hair and a blue shirt behind her.
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