When Peter drives his malfunctioning car into the Firehouse, all the others stand next to Ecto-1, which is propped up for repairs. but when Peter's car explodes, Ecto-1 is nowhere to be seen.
When Egon explains that WWII was a boom time for Gremlins, Winston's uniform has Egon's color by mistake. It still has Winston's trimmings. The same thing happens after Peter says "Piece of cake".