On A Clear Day I Can't See My Sister - S16-E11
Continuity mistake: In Sprawl*Mart, the handle on the shopping cart disappears between the time Grandpa pulls the cart loose, and when you see him riding inside the cart.
On A Clear Day I Can't See My Sister - S16-E11
Continuity mistake: For "On a Clear Day, I Can't See My Sister": Throughout the episode, the backyard alternates between having a fence at the end and a forest at the end.
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