The Two Mrs. Nahasapeemapetilons - S9-E7
Continuity mistake: When the garden is seen with Bart throwing Hymns into the fire Apu's mother starts to walk to him and she must walk through a curved green structure.In the next shot of Bart,the structure has gone.
The Two Mrs. Nahasapeemapetilons - S9-E7
Continuity mistake: When we see the garden and Bart throwing Hymns into the fire the large tree is fully green. After the shot of Bart,the camera goes up and we see branches with no leaves on them though.
The Two Mrs. Nahasapeemapetilons - S9-E7
Continuity mistake: When Apu walks down the isle the early shots show that Bart and Lisa are not amongst those either side.When Apu walks by,the shot goes to the ground and they have now appeared.
The Two Mrs. Nahasapeemapetilons - S9-E7
Continuity mistake: The amount of liquified chips in the bag at the home changes depending on the shot.
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