Continuity mistake: In episode 10 (Joey's Place) the Tanner family move Joey into the garage, redecorating it so the entire place is filled with Joey's furniture, but in this episode it shows the characters in and out of the garage which is completely empty and back the way it was before Joey moved in. Later in the episode Joey's stuff is out of the alcove again.
Visible crew/equipment: In the the episode "In-console-able" from series 19, in the kitchen when Paul accidentally puts custard and hundreds of thousands on a dinner, he puts the lid on it and when the camera zooms in you can see a cameraman with a camera recording and Barry getting ready for his take.
Revealing mistake: The "hostage" episode reuses footage from the "Dinosaur" episode, which doesn't totally fit. When the giant crabs attack and destroy the group of houses on the island, the longshot of the damage is recycled from the earthquake episode - including an earth fissure, something the giant crabs wouldn't and probably couldn't have done.