Margical History Tour - S15-E11
Plot hole: During the Mozart skit, Lisa puts a sleeping tonic in the emperor's wine, but when she drank it she fell asleep also. How could that be if she only poisoned one glass of wine and it was the emperor's?
Margical History Tour - S15-E11
Factual error: Lisa, as Salieri, says she has wine for sale : "Claret, Port, Riesling ...". All three glasses on her tray are filled with red wine. Riesling is a white wine.
Margical History Tour - S15-E11
Continuity mistake: Lisa empties a glass of red wine that she previously poisoned with sleeping potion. When she falls over sound asleep, her glass is shown on the ground next to spilled wine.
Margical History Tour - S15-E11
Continuity mistake: In the Mozart sketch, the music Bart writes with his foot and then picks up suddenly vanishes in the next shot.
Margical History Tour - S15-E11
Factual error: On the castle where King Henry VIII is supposed to live, the flags at the top have the pattern of the English flag, being a + shaped cross on a coloured background, but it should be a red cross on a white background. Instead it's a white cross on a blue background. Those are the colours of the Scottish flag, but England and Scotland were separate countries at that point in history. And the cross on the Scottish flag is an X shape rather than a + shape anyway.
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