Elementary School Musical - S22-E1
Other mistake: As Stephen Hawking rotates in circles, his front wheels stay locked in a straight position, rather than turning into the turn.
Elementary School Musical - S22-E1
Other mistake: As Lisa and Marge drive out of Brooklyn, they see a mural painted by the two artists. As the camera looks at Lisa, the mural reflection should be reversed, but isn't.
Other mistake: After Lisa has made Bart leave the baseball team, Lisa and the rest of the baseball team are having pepperoni pizza at Luigi's. Lisa is also eating the pepperoni pizza. However, Lisa is a vegetarian, so why would she eat pizza with meat on it?
Treehouse of Horror XXI - S22-E4
Continuity mistake: In the second segment, after Roger has told them about what happened to him, a radio appears out of thin air.
Treehouse of Horror XXI - S22-E4
Continuity mistake: In the second segment, as Roger is telling them about what happened to him, as he finishes the story of Marge and Homer saving him, in his recount Marge is wearing a shirt and bikini bottoms (the shirt is covering the bikini bra). But when they saved her, she was just wearing a bikini.
Continuity mistake: Mr. Burns attempts to plan revenge on Springfield by placing The Town in a dome. However when Lenny tells Burns it has already been done, Mr. Burns tells the helicopters to stop placing the dome. In this shot, both Burns' helicopter and the helicopters placing the dome are the same height off the ground. But in the following shot, the helicopters are now 50 feet above Burns' helicopter. (00:18:55)
How Munched is That Birdie in the Window - S22-E7
Continuity mistake: Right before the Itchy and Scratchy Show episode starts, Santa's Little Helper is colored in a much darker shade of brown than usual.
Continuity mistake: In the scene where Smithers is showing Burns the bar, Smithers is in his grey suit. When Burns turns to talk to Grizzly Shaun, Smithers is wearing his standard green jacket and bow tie. Afterwards he is back in his grey suit.
The Blue and the Gray - S22-E13
Audio problem: When Homer says "Drive my kids to school?!" his mouth is out of sync with his voice.
A Midsummer's Nice Dream - S22-E16
Continuity mistake: The seating arrangements during the Cheech and Chong show keep changing between shots. Smithers is first seen sitting between Patty and Luigi, then he is between Louie and Legs, and then he is between Patty and Luigi again, then finally, he is sitting next to Mr Burns. And Miss Hoover is at first two rows in front of the Simpsons, then she is a row behind them when Homer is going to the stage.
Continuity mistake: Near the end when Homer is going into the show, he is not holding his coat. Then it appears in his hands and gets stolen. In the very next scene, he then wears his coat again. (00:19:40)
Other mistake: In the credits, Kristen Schaal is misspelled Kristen Schall. (00:20:40)
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