Character mistake: Humphrey tells the riddle of the two barbers wrong; you have to set it up saying that the 'good' barber has a great haircut, not that he's great at cutting hair, or you negate its point (which is that the 'bad' barber with the bad haircut is the one who did the haircut to the good-looking barber, and vice-versa).
Continuity mistake: Humphrey, triumphant for the discover made through his gossip with the roomie of the suspect, slams the yachting magazine on the desk with a swift motion of his right arm, which is the left arm in the next shot. (00:37:25)
Continuity mistake: Early morning at the station. Florence just arrived, and Humphrey is telling her about his suspicions on Nicky Hoskins. She replies that she needed the job; between shots there's an obvious difference in the positions she listens in. She is palm to back at first, then both palms upturned. (00:36:50)
Factual error: The website of the toy manufacturer has as address for its store a location in Harrogate, but the ZIP code has an incorrect format, with the 4th character being an O and not a zero, and HG4 being the neighbouring Ripon. (00:28:30)
Other mistake: It's played as a gag, but still it's quite inconceivable that in "fifteen minutes" it would get pitch dark so that Dwayne can avoid his duties sanding the ship! How much time could he have bought even if he had more excuses up his sleeve? Goodman really can't tell the difference between 15 minutes and a couple of hours? The scene started when it was nowhere near dawn. (00:21:10)
Continuity mistake: On the derelict boat, Humphrey invites Dwayne to do some sanding together, but Dwayne has a counterproposal. Humphrey listens to it with his hand on his hip, away, on the hip again. (00:21:15)
Continuity mistake: Dwayne points his finger at JP telling him his former superior said "a policeman can't have any weaknesses." Reverse shot, and Dwayne's hand is nowhere in sight, but it is a moment later. (00:16:30)
Character mistake: The rap sheet of Laura Hagen's dad says that he served "half of an 12 years sentence." An twelve? (00:15:50)
Continuity mistake: Dwayne mentions enlisting the help of the Saint Marie diving school. At the following cut, his shirt is more open, revealing more of his trademark tank, and he is holding the notepad where it would have been visible in the close-up. (00:09:55)
Continuity mistake: Humphrey and Florence go back on the boat after the preliminary interview. Florence is on the phone with the Coast guard when she gets on the boat; the phone is on her left hand, and the right hand is occupied by the notepad. When she tells Humphrey the coast guard's report, they have traded places. (00:09:20)
Continuity mistake: Laura Hagen is back in the cabin to retrieve the sample bag she forgot. The bag was under a map on the table, which she moves by a whole lot...or just a tiny bit, when the table is shown from another angle. (00:02:25)
Other mistake: Commissioner Selwyn Patterson puts some pressure on Humphrey and the team saying that "a wealthy tourist has just been killed." But Dan Hagen was not a tourist; he lived on Saint Marie with his wife, as said by the fellow oceanographer Jonathan Taylor, and they have a villa. Someone as well connected and nosy as Patterson wouldn't miss the notion of a multimillionaire living on the island. He also says that he needs to reassure the yacht club that there are no pirates in the area, but it was already established by the coast guard that no ships approached the area. (00:12:15)
Answer: There's probably no particular reason. Sets and props on long-running TV shows often change as needed and for various reasons throughout a series run.
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