Revealing mistake: When Frasier comes into the chalet after skiing he doesn't show any of the visible effects after a hard day on the slopes. Meaning, his face isn't even flushed from the cold, his hair is perfectly combed after wearing a hat and there is not even a drop of snow on his boots.
Plot hole: Laura successfully knocks out both bad guys, steals their van and crashes through the warehouse doors. The van doesn't stall, but inexplicably, she stops it, gets out and runs away on foot, even though the baddies are coming to and coming after her. Not the option you'd expect a kidnap victim to choose: most people would floor it and keep on driving. (00:23:40)
Other mistake: T.J. Hooker and Vince Romano pursue two men who robbed the box office during a Beach Boys concert. The action takes place in the lobby of the Los Angeles Sports Arena, which is an indoor venue, but the footage of the Beach Boys performing is from an outdoor concert.
Audio problem: In the first scene, we see a quartet led by a sax player. The music we hear, however, is of a trio without sax. This is fixed in the rebroadcast where the song is Satin Doll led by the sax. Additionally, the piano now sounds like an electric to match its look.
Factual error: There is an intercom system in the library that is used by Derek (and at the end, Edward). They try pushing down the buttons to talk (which is normal for intercoms), but then each time, we are hearing Ricky and his grandfather's conversation from inside the car that's outside without using the intercom connected to the house. In the 80s, a house intercom system would not pick up a conversation in a parked car outside.
Factual error: Doris finds out that Gypsy Queen "Lisa" died from influenza around 1918, so she didn't get to star in her performance. However, when Doris and Lisa's ghost are singing their duet later, Lisa's hair and costume are 1980s style, instead of the era she died.
Factual error: The forces of Cassiopeia all sport the crown-like "W" sign which is the shape of that constellation... but only as seen from earth! These five points in three-dimensional space (like all star signs named after anything) look like that when viewed from our own planet; but from anywhere else, they aren't shaped like that at all. Why would they chose to see themselves through a very specific angle of view from some other distant planet (earth)?