Other mistake: When Cat picks up the can of Leopard lager which is invisible to Lister, he shakes it, pops the cap and sprays Lister with foam. The foam is visible but the can remains invisible, and that makes no sense. If we are seeing the scene from Cat's point of view the can and foam should both be visible, and if it is from Lister's then neither should be.
Continuity mistake: When Roseanne & Jackie talk about Arnie, they act like they haven't known him long. Jackie even states, "I don't know him." Yet, in episode "Why Jackie Becomes a Trucker," Jackie sleeps with Arnie. Roseanne says all the girls made a pact in high school that none of them would ever sleep with him.
Plot hole: When Kevin is upset about Paul leaving for summer and is just lounging around the house, he asks why they can't go on vacation. His mom says "Maybe next Summer." In the very next episode, which takes place in the same Summer, they are going on a "traditional" Summer vacation.
Factual error: When Pug comes home, Rhoda puts on a Christmas record. The record player has an automatic changer that drops the disc and then moves the arm into place. Though a small 45 rpm changer was designed as early as 1938, and this movie's set in 1942, the type Rhoda uses here wasn't around for another 20 years. (00:09:00)
Continuity mistake: "The Feverman": Before putting the chain around his neck, the doctor removes both his detachable collar and his black string tie. A few shots later, not only is the collar back, but he's now wearing a red ascot-style tie. Both collar and tie vanish again one shot later. (00:17:05)
Factual error: About 45 minutes into the episode, the girls' car stalls because the alternator's wire has been removed to cause this. For a car to stall like this, the battery has to be heavily drained which it would wind up being. When the killer comes up to the car, he tells her to try and start the car. She does and it turns over but doesn't start. The battery would never have enough amperage to turn over the car if it didn't have enough to keep the motor running.
Visible crew/equipment: In episode 1, "Computer Logic", there's a scene in which Austin & Michelle step into a computer convention, where a hot-shot software designer, Mr, Blaine, is delivering a sales pitch from his wheelchair. In one shot the boom microphone can be seen dipping deeply into frame.