Continuity mistake: In the scene where Max dumps the slushee, the cup was filled way over the top with slushee. When he turns the cup to dump it, the slushee is now down way below the top of the cup. (00:32:30)
Continuity mistake: After Lisa's creation, in the car Wyatt's left hand is resting on the back of Lisa's seat, but when Lisa asks why Gary chose the name Lisa, Wyatt's hand is gone, only to reappear and disappear again depending on the angle of the shot.
Revealing mistake: There is a visible cord pulling the couch during the scene where furniture is sucked out the chimney. (00:55:50)
Continuity mistake: After Lisa is created, a poster in the bedroom is ripped. Later, before the house is restored, the poster is whole again. (00:14:10 - 00:59:40)
Other mistake: When Chet is getting on everyone's case about everything that is wrong with the house, he says to Lisa, "I didn't think it was a whale's d__k, honey" in reference to the missile going through the house. The French subtitles has "bitte" to mean the portion of the male anatomy. The correct French word is "bite". "Bitte" means either "bite" or "bollard" in English. (01:14:10 - 01:16:10)
Audio problem: At the bar when they're leaving, Anthony Michael Hall's mouth doesn't match up to anything being said.
Visible crew/equipment: During the party, Deb and Hilly join Gary and Wyatt in the bathroom, and when the boys step into the shower enclosure and close the glass door, a crewmember's moving reflection is visible on the shower head.
Continuity mistake: During the creation of Lisa, in some shots Gary is wearing a baseball cap and in others he is not. (00:07:30)
Revealing mistake: Wyatt's grandmother is supposed to be frozen solid, however she moves a bit when we see them in the closet.
Revealing mistake: When Gary is being chased by the police, a stunt double in a blond wig is driving his car. (01:20:35)
Factual error: When Anthony Michael Hall is being pursued by the police, they have the logo of City of Los Angeles, but this takes place in Chicago. (01:18:40)
Continuity mistake: At the party, Deb changes from having bright red lipstick to a subdued color. (01:06:50 - 01:12:30)
Chosen answer: They probably only had permission to use the song at the cinema and take home releases, so when shown on broadcast TV they'd have to use another song.