Flintstones 2: Viva Rock Vegas - The Chips Are Down
If you've managed to sit all the way through this awful movie, in the finale scene with all characters singing in a long chorus line, the evil character Chip starts off on the end of the line, disappears when the shot changes to a different angle, and then reappears for the long shot. Where did he go? Not to acting class at least.
You beat me to this. And ALL the way through the credits. After them is a slide ad for the Univershell studios telling you to visit while in Hollywood!!