Other mistake: When Homer talks to Bart and Lisa through the window, he is standing almost straight up, but considering he is right in front of the TV in the next shot, he would've had to crouch down a little. (00:03:50)
Other mistake: When Homer leaves the window, the TV is in a different area of the living room. (00:03:50)
Other mistake: In the shot before Marge says she will marry Homer, the right side of the screen is cut off a little. (00:08:25)
Other mistake: When Marge sees the letter from Homer, she says "You won't see me again until I'm a man." On the paper though, it reads 'But you will not see me-' and the sentence is cut off, and the rest of the paper is blank. (00:16:10)
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