"Beyond the Farthest Star", the first episode aired of Filmation's "Star Trek: The Animated Series" (TAS): Arex is navigator and Sulu is helmsman, with Kirk in the command chair. Uhura's chair is vacant.
Seconds later: suddenly, a redshirted Chekov(?) is navigator - and Uhura is back in her usual chair.
This brief sequence is perhaps a re-use of part of some TAS pilot/test bridge footage, maybe before they were certain the budget couldn't afford Walter Koenig's voice, and before Arex was conceived. Note that "Chekov" is even in red, a precursor to his proposed role in "Star Trek: Phase II", as security chief (a Chekov "Phase II" redshirt uniform was auctioned off diring the "It's a Wrap" eBay auctions of Paramount costumes and props) and, of course, came to fruition in ST:TMP.
Okay, so maybe they accidentally threw Scotty into the scene but...
Seconds later again: Arex is back, as the bridge shakes!
(It's fun to speculate. It's certainly not the only blooper in TAS.)