The Great Bank Robbery - S4-E6
Revealing mistake: The bandits lock Bo and Luke inside closed coffins and then leave. Bo and Luke begin "rocking" the coffins back and forth to tip them over so they can escape. However in the following shots, as Luke is rocking inside his closed coffin, the camera slips or shifts too much, and you can see the barns' interior at the sides of the screen, alongside some equipment.
Revealing mistake: "Dr. McDee Must Die" (Adventure 5, Part 3): When the champagne glass shatters in front of Sapphire, you can see the mini explosive charge used to break it. It lands on the table among the glass shards. (00:10:00)
Revealing mistake: When Lizzie awakens on the morning that Edith gets released, Edith doesn't respond and Lizzie goes to her bed to "mourn" the passing of her friend. Except that Edith is still breathing.
Winds of War - S1-E8
Revealing mistake: When the widow is bandaging the fighter pilot, the part of bandage she is wrapping appears and disappears during the animation - when her hand movies, instead of adding new layers of bandage, the army causes the green sleeve of the space suit to flash back in view. (00:20:10)
Return of the Fighting 69th - S1-E6
Revealing mistake: Before Roxanne Trent hits the box, it is possible to see that her hand is normal, not iron. (00:17:01)