Catch 'em If You Can - S15-E18
Continuity mistake: When Homer and Marge think they have finally got away from Bart and Lisa and Homer is about to look in the dinner bowl, on the table holding the food there is a bottle of champagne and two glasses, yet when Bart and Lisa jump out the 3 things have vanished. (00:17:20)
Catch 'em If You Can - S15-E18
Continuity mistake: When Bart, Lisa, Homer and Marge are on the ferris wheel near the end, we can see in one shot the person behind Lisa has blonde hair, and then in the next shot the person has black. (00:18:45)
Catch 'em If You Can - S15-E18
Continuity mistake: The Credit card numbers for Ned and Rod's VIZA cards are exactly the same: 8525 4941 2525 4158 First Bank of Springfield Viza valid from 1/1 to 12/31(thirty years on the credit card?)
Catch 'em If You Can - S15-E18
Continuity mistake: When Lisa says "It's called Wicca, and it's empowering" to Bart, her necklace is red instead of 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