Factual error: Despite the fact that other officers are doing so, Columbo does not wear gloves while examining the crime scene. He also eats and drinks in the room - both absolutely forbidden - leaving eggshells scattered about the place. The crime scene is now totally compromised and nothing found can be used as evidence.
Undercover - S12-E3
Factual error: At the crime scene, the landlady of the dead man is brought into the room in order to identify one of the dead men. This is never, ever done - she could contaminate the crime scene in a dozen different ways. She would be asked to identify the corpse at the morgue after the scene had been cleared by forensic examiners.
Suggested correction: Completely wrong. Immediate identification of a murder victim is vital to the continuing investigation. As long as the landlady was under escort (she was) and did not touch anything in the room (she did not), she would definitely be asked to identify the dead man. There are too many examples to list, but when actor Bob Crane was murdered in 1978, his theatre co-star Victoria Berry was escorted onto the crime scene to confirm the identity of the dead man - Crane.
Undercover - S12-E3
Continuity mistake: Columbo ushers Krutch and Susan into an office for questioning. When he closes the door, the venetian blinds on it change from straight to misaligned and back again between shots.
Butterfly in Shades of Grey - S12-E2
Other mistake: Fielding Chase and Lieutenant Columbo are on a road in the mountains above Malibu and Chase's car will not start. He tries unsuccessfully to call the Automobile Club on his mobile phone. He tells Columbo the phone number is "555-4411" but each time he tries to call, he presses nine digits.
Butterfly in Shades of Grey - S12-E2
Continuity mistake: From his estate, Fielding Chase looks toward his front gate and sees smoke coming from the engine of Columbo's car. When we see Columbo standing atop the car and yelling for Chase to open the gate, there is no smoke.
Undercover - S12-E3
Continuity mistake: When Krutch speaks to Columbo on the phone about 40 minutes into the show, his voice sounds like he has a cold. Earlier and later in the show, his voice doesn't sound like that.
Butterfly in Shades of Grey - S12-E2
Other mistake: Jerry Winters' mantel clock chimes four times but the clock shows the time as 3:59.