Death Hits the Jackpot - S11-E1
Continuity mistake: After Lamarr takes off Freddy's undershirt we see the level of the water in the bathtub. Then he drags Freddy over to the tub and breaks his watch. At that time the water level is lower than it was before, even though the water was still running.
Revealing mistake: At the end when Laurel and Hardy are licking Columbo, a substance is caked on Columbo's neck, presumably the food they used to get the dogs to lick Peter Falk.
Other mistake: Kingsley doesn't know if his victim is married or unmarried, whether or not he has children, if he has a maid, but he brings a hand vacuum and empty vial to the murder to collect cat hair from the victim's cat to plant on Clifford's jacket.
The Bye-Bye Sky High I.Q. Murder Case - S6-E3
Factual error: A "silencer" (properly called a "suppressor") does not muffle a gunshot to a whisper. An unsuppressed gunshot is about 160 dB, equivalent to a jet airliner taking off, but a suppressed gunshot still registers about 100 dB, equivalent to a power lawn mower. Also, a suppressor on a revolver is totally useless, because most of the noise comes from the gap between the front of the cylinder and the rear of the barrel.
The Most Dangerous Match - S2-E7
Factual error: Clayton tells Columbo that he had purchased a new transistor for his hearing aid. Hearing aids - even the old types in use in the 1970's - do not have any user-replaceable parts. The only thing that can be replaced is the battery.
Other mistake: Several of the English characters change back and forth between calling Columbo "leftenant" and "lootenant."
Other mistake: When Benedict puts his briefcase in the back of the Jaguar, the hatch does not close properly. It is still not closed properly when he picks up the car from the repair shop.
Murder with Too Many Notes - S13-E4
Other mistake: In the movie within the story the murderer repeatedly stabs the victim and pulls back the knife. Even after several stabs there is no blood on the knife.
Factual error: Columbo asks for a red wine. His host orders a Beaujolais but the butler brings a Bordeaux. Beaujolais is from Burgundy, not Bordeaux. (01:18:40)
Dead Weight - S1-E4
Other mistake: Columbia calls Helen Stewart from a pay phone. He dials only six numbers, not seven.
The Most Dangerous Match - S2-E7
Other mistake: The police photographer takes a picture of the garbage grinder. His camera has a flash, and the photo is indoors, but the flash does not fire.
Character mistake: In the grocery store scene Robert Culp sits on a display of pumpkins but there are 2 signs that say watermelons.
Suggested correction: As a retail worker of 18 years, I know that POS (signage) mistakes happen in supermarkets, for example a product is moved and the correct POS is not replaced. This scene seems to be filmed in a real supermarket meaning this is not a mistake made by the show's producers, however if this was filmed in a studio, "Character Mistake" would be the wrong category as the mistake would have been made by the set designers.
While I've never seen mislabeled items I know mistakes can happen. But since the characters aren't real, every mistake they make is the fault of someone on the crew, whether it's the actor, writer, or set designer. For example, misspellings are considered character mistakes (unless intentional), even though it would have been made by the person who created it.
Character mistake: This episode opens with James Ferris typing the final chapter of a mystery novel. He is using all-capital letters, No professional writer would do that.
Suggested correction: It's not meant to be all capital letters, but block letters. Just look at the title card and credits in the opening - they're block letters too.
Continuity mistake: There are several views of Uncle Jarvis in his (beautiful) Bentley S2 Continental from the front. We see the inside rear-view mirror, and it is correct. When we see him spot the police behind him through the mirror, it is a different mirror and not the correct one for that car.
Character mistake: After Columbo disturbs Dr. Kepple and his ball goes in the rough, Kepple says they are playing for rather high stakes. He picks up his ball, looks at it, and places it back on the ground. In a high stakes game, that would be cheating, and the other players would not have tolerated it.
Factual error: Several times, the revolver used to murder the singer is referred to as a "Weatherby" or "British Weatherby." Weatherby is an American manufacturer of rifles and shotguns; they do not make handguns. The revolver used is a Webley, which is of British manufacture.
Continuity mistake: At the cafe when Columbo talks with the police officer his cigar is in his hand in the back shots but disappears in the front shots.
Character mistake: Kingsley carries a briefcase in to the attorney's office, but leaves without it.
Caution: Murder Can Be Hazardous to Your Health - S10-E2
Continuity mistake: When Sheba the dog scratches Anders' car her claws are on the glass and the top of the metal part of the door, above the character line. In the photo that Columbo shows, the scratches go much further down the door.
Character mistake: Columbo took the Beretta off the gun display by inserting a pencil into the barrel of the gun. In a previous episode, he said to NEVER insert a pencil there because it will ruin the groove of the barrel, making it impossible for ballistics to get a match on the bulletin. When using a pencil, Columbo picks up a gun up near the trigger.