Continuity mistake: In the scene where Homer decides he wants to stay with Lurlene, she locks the door about 3 times before going to kiss Homer, but when Homer leaves, he just opens the door, he doesn't unlock anything.
Continuity mistake: After Lurleen sings 'No-One Understands You', she puts on her apron and picks up a tray. On the tray, there are three bottles of beer. But in the next shot, Homer goes over to Lurleen, and there is only a cup. (00:07:15)
Continuity mistake: When Homer and Marge are entering the cinema, Marge is taking Maggie with her. But when watching the film, Maggie is nowhere to be seen.
OL1V3R666
Continuity mistake: When the family are driving home from the cinema, Bart draws an angry face on the back of Homer's head. It is never there at any other point in that night.
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