Hoffa (1992)

Revealing mistake: Very poor diopter work on the Las Vegas stage: the audience is "split in half", one part very blurry behind DeVito's head, and the other half crisp and clear.

Revealing mistake: Several times in the movie you can see really poor backdrop work, such as the stars in the opening scene, the hunting scene in the woods, the Capital building from Hoffa's office and from Kennedy's office, the truck line towards the prison, and a few others.