The Mook, the Chef, the Wife, and Her Homer - S18-E1
Continuity mistake: Just as Otto is about to put in the grand funk tape you can briefly see an different tape in the recorder. Slow motion is not needed but a sharp eye is.
The Mook, the Chef, the Wife, and Her Homer - S18-E1
Continuity mistake: When Bart and Fat Tony's accomplices are going to meet Krusty, Krusty's nose can briefly be seen as white when it should be red.
The Mook, the Chef, the Wife, and Her Homer - S18-E1
Revealing mistake: When Fat Tony says "The Calabresis. My archenemies in waste management." while driving the carpool, a huge line briefly appears around his cheek and mouth.
The Mook, the Chef, the Wife, and Her Homer - S18-E1
Continuity mistake: When Lisa grabs Ottos tape recorder her necklace is orange but when she gets off the bus it is white.
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