Homer vs. Lisa and the 8th Commandment - S2-E13
Continuity mistake: When all the kids run out of the back door, Homer drops a blue box. In the next shot it is a yellow box with red lines on the edges.
Homer vs. Lisa and the 8th Commandment - S2-E13
Continuity mistake: When Homer and Marge are discussing about unhooking cable, the time on the clock on Homer's bedside table changes between shots.
Homer vs. Lisa and the 8th Commandment - S2-E13
Continuity mistake: When all the kids are watching TV, we see Wendell, Martin and Milhouse. Absurdly they appear to be right below the ceiling in this shot - when in every other shot they are sitting on the sofa or standing.
Homer vs. Lisa and the 8th Commandment - S2-E13
Continuity mistake: In every other episode, the bar at Moe's Tavern is a regular L-shape. In this episode, it has somehow gained two additional angles on the long side, making it a Z-shape (plus the angle to the short end, which is not shown).
Homer vs. Lisa and the 8th Commandment - S2-E13
Continuity mistake: At Sunday school, Milhouse's jumper changes from black to red between shots.
Homer vs. Lisa and the 8th Commandment - S2-E13
Revealing mistake: When Homer is imagining being locked in the jail cell and he turns around to find he is in his own home, he turns to look at his family. There is a close up shot of his terrified face, and the people in the background watching the game (I think it might be Lenny and Carl) have no eyes. The rest of their face is fine, but their eyes are missing.
Homer vs. Lisa and the 8th Commandment - S2-E13
Continuity mistake: When Bart and Lisa are at Sunday school, the teacher writes "HELL" on the board, which changes from being red to black between shots.
Homer vs. Lisa and the 8th Commandment - S2-E13
Continuity mistake: When Homer is sitting watching cable, the rest of the family comes home and one of them is carrying a plant in a pot, which is put down next to the couch. While they watch and watch cable, it grows very tall and then withers down. When Homer goes behind the TV and starts kissing the wires, the plant has moved to next to the doorway and is suddenly fully grown again.
Homer vs. Lisa and the 8th Commandment - S2-E13
Continuity mistake: When the family are outside, in the shot just after Homer says "At the worst possible time" you can see the living room - everybody has disappeared in that shot.
Homer vs. Lisa and the 8th Commandment - S2-E13
Continuity mistake: When the door is answered to Mr Burns and Mr Smithers, Barney is seen answering, who has orange sleeves. However when the door is opened, you can just make out a white sleeve, which could be none other than Homer's.
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