10 Times Star Wars Filmed Things You Weren't Meant To See
2. Samuel L. Jackson's Totally Unconvincing Stand-In - The Phantom Menace
Among other things, The Phantom Menace concludes with Palpatine (Ian McDiarmid) being elected Chancellor, but if you keep your eyes peeled when he greets Padme (Natalie Portman), a not-so-recognisable Mace Windu (Samuel L. Jackson) is visible in the background.
For whatever reason, Samuel L. Jackson wasn't available the day that the scene was being shot, and so a stand-in was instead drafted in to fill his spot.
Presumably George Lucas assumed audiences would be too focused on Palpatine and Padme to notice, but of course, between the obsessive proclivities of Star Wars fans and the benefits of higher-definition releases in recent years, the impostor Mace Windu sticks out like a sore thumb.
It would've been a lot simpler to just... keep Mace out of the sequence if Jackson wasn't available, considering that the character simply walks on by without doing anything plot-specific.