Four Regrettings and a Funeral - S25-E3
Continuity mistake: At church, while Marge is reminiscing about being pregnant with Bart, Kirk Van Houten is seen with grey hair and eyebrows. He has his ordinary blue hair and eyebrows in all other shots of him.
White Christmas Blues - S25-E8
Continuity mistake: While Mayor Quimby is giving his speech, Moe is in two places at once. He is simultaneously standing next to Mayor Quimby and amongst the crowd of people.
Continuity mistake: When the students have to practice square dancing in the gym, Lisa spots a male student and there is a red circle next to her on the floor where she is standing. When the teacher tells Lisa she has to dance with groundskeeper Willie, the circle has disappeared.
Continuity mistake: When Lisa arrives home after her parents gave the boy a party, she parks her bicycle near the path. When Lisa sees the boy with make-up on his face in the next shot, the bicycle is on the grass.
Continuity mistake: When Lisa and Tumi are listening to the radio in Lisa's bedroom, the door behind them changes position between shots.
Continuity mistake: When Lisa and Tumi have finished their square dancing, there is nothing to the left of the basketball stand, but when Lisa and Tumi are talking in the next shot, three balls have appeared.
Continuity mistake: When Homer reveals the murderer in the story, he is holding a card in his right hand. When Booth tells Homer he has given away the game, the card has disappeared.
Continuity mistake: When Marge and Maggie check out their groceries at the supermarket, the cashier says that she requires a price check on Gramma Shortcut's Store Bought Bundt Cake. The position of the cake on the scanner changes between shots.
Continuity mistake: In a full view of the checkout, when the cashier requires a price check on Gramma's Shortcut Store Bought Bundt Cake, you can see beside Marge there is a stand and there is a man with a beard and glasses behind it. When we see Marge in the next shot, the man is now standing behind her, and there is also a couple who weren't there previously.
Continuity mistake: When Marge puts down a dollar note on the scanner and takes the cake before leaving the supermarket with Maggie, the position of the dollar note on the scanner changes between shots.
Continuity mistake: When the man is talking to the cashier in the supermarket after Marge and Maggie left, there is a dollar bill on the scanner. When the cashier tells him to "shut up", the dollar bill has gone.
Continuity mistake: In a full view of Ear Poison on the stage at the block party, there are two guitarists next to the drummer, who were not next to him in the previous shot.
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