Burns Verkaufen der Kraftwerk - S3-E11
Other mistake: After the scene where Mr. Burns gives Smithers his picture of him and Elvis Presley, Homer asks Lisa a couple of questions about Germany. At the beginning of this brief scene, Lisa is reading a book, and from her point of view, her eyes are moving from right to left, which shows she is reading the wrong way on a single page. (00:11:10)
Burns Verkaufen der Kraftwerk - S3-E11
Other mistake: When Burns is writing on the back of the big cheque, the writing suddenly appears in one block. (00:10:05)
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