Wild Barts Can't Be Broken - S10-E11
Audio problem: When Lisa is broadcasting secrets about Springfield residents in a British accent, her lips don't match her mouth at all.
Sunday, Cruddy Sunday - S10-E12
Continuity mistake: When Homer gets the coupon book, look at the plant on the wall. It changes position between shots.
Sunday, Cruddy Sunday - S10-E12
Continuity mistake: The desk in the car repair shop behind Homer changes positions between shots.
Audio problem: At the end where Homer is carrying Mark Hamill out of the theatre, Mark's lips don't match with what he's saying.
When You Dish Upon a Star - S10-E5
Revealing mistake: When Homer and the family are having hamburgers at the dinner table, at one point you can see the oven. The pointer on one of the dials is misaligned.
Audio problem: When the radio is playing "Wannabe", the song stops but Homer doesn't touch the radio.
Simpsons Bible Stories - S10-E18
Continuity mistake: When Bart is trying to wake up Homer, Maggie is seen with a blue pacifier. In the shot after the next, Maggie's pacifier is red.
Continuity mistake: When Ralph comes to see Lisa, she is wearing her turquoise slippers. However, after he leaves and she drops the book on the floor, her slippers have gone.
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.
Monty Can't Buy Me Love - S10-E21
Continuity mistake: Ralph Wiggum is seen riding the train inside the mall, but is seen some seconds later amongst the crowd of people still waiting to enter the store.
Monty Can't Buy Me Love - S10-E21
Continuity mistake: Bart is next to Homer when Marge says "Where did you get that champagne?", but in the next shot, a clown is in the spot Bart was.
The Old Man and the C Student - S10-E20
Audio problem: At the end of the episode, Grampa's mouth doesn't move when he sings.
Wild Barts Can't Be Broken - S10-E11
Continuity mistake: During the song, Reverend Lovejoy at first has a blue sweater over his usual pink shirt, then he has a blue shirt, then he has his pink shirt without a sweater.
Wild Barts Can't Be Broken - S10-E11
Continuity mistake: When Dr. Hibbert says "Go ahead, girlfriend" at The Town hall, he is wearing a blue sweater, in the very next shot of everyone talking, he is wearing a pink sweater.
Wild Barts Can't Be Broken - S10-E11
Revealing mistake: Lenny's lower torso disappears for two frames when he, Carl, Homer and Barney are singing "We Are The Champions/We Will Rock You."
Thirty Minutes Over Tokyo - S10-E23
Continuity mistake: When Database is at The Java Server, he is using a teal computer, but when Snake comes in, he is using an orange computer, then he is using a teal computer again.
Revealing mistake: Two kids in the middle of the class do not have a test. However, they are shown writing on their desk as if they had a test paper.
Marge Simpson in 'Screaming Yellow Honkers' - S10-E15
Continuity mistake: When Eddie the cop (as Curtis E. Bear) is being bludgeoned with 2x4's at traffic school, Krusty's nose is the same color as his skin instead of being red.
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