Continuity mistake: Kermit's ice cream in the fair scene changes colour.
Continuity mistake: In the scene where Kermit, Fozzie, and the gang are following Gonzo, who is floating from the helium balloons, Fozzie opens his door and looks up at Gonzo. When he comes back into the car after Kermit shouts at him to do so, the steering wheel comes loose from the dash and all the Muppets start yelling at him for being reckless. In the next shot of the interior, the steering wheel is back in place. I do feel maybe this was a blunder that was left in on purpose, because it was so funny the way all the puppeteers ad-libbed a reaction to what shouldn't have happened, but it fails in continuity because in the next shot the wheel is fine.
Continuity mistake: When Kermit and Fozzie come round the corner and see the billboard with Kermit's face on it, you can see that there is nothing behind the billboard. Yet later when Doc Hopper and Max are leaving, Hopper's car is behind the billboard. The car slightly sticks out, so Kermit and Fozzie should have seen it.
Continuity mistake: When Kermit and Fozzie meet Big Bird, their car stops about fifteen feet behind him, at the end of some dark tire tracks. But when the camera looks at the pair in the car, they're looking directly at their left, and Big Bird converses with them looking to his left in quarter profile to them. When they leave, their position is about ten feet back from the end of the marks, a good twenty feet from where they originally stopped.
Continuity mistake: After Kermit is tossed over the crowd in the El Sleazo, he catches on a ceiling fan, and it swings a bit from the impact. After a shot of the bartender speeding up the fan, it is no longer swinging. This is impossible with any weight on one blade. When Kermit is slung off the fan, you can see the fan is not on at all, Kermit is at the piano, and just about everybody in the place is still looking at the fan.
Continuity mistake: The crack in Fozzie's Studebaker windshield comes and goes throughout the film.