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.
Prisoner: Cell Block H (1979)
1 revealing mistake in Season 1 generally
Starring: Betty Bobbitt, Elspeth Ballantyne, Maggie Kirkpatrick, Sheila Florance
Deliberate mistake: After MacNelly enters the ladies room to confront the red haired lady, she shoots the woman in the chest, but there's no gunshot or bullet hole or blood anywhere. But the red haired lady dramatically collapses to the floor. Then during a closeup, glances upward at MacNelly, and then her head droops downward.
Bea Smith: I'm going Freak-hunting.