Episode #3.4 - S3-E4
Continuity mistake: At the concierge during the first interview, the phone rings. Simone asks "May I?" pointing with her left hand, which becomes the right hand after the cut. (00:09:00)
Episode #3.4 - S3-E4
Continuity mistake: Summing up the lack of progress in the case in front of the whiteboard, Humphrey points at Bevans' picture with his right hand at first in the overhead shot, which becomes the left hand at the cut. (00:25:30)
Episode #3.4 - S3-E4
Continuity mistake: When Humphrey foolishly lets Catherine pick the dish for dinner, he lifts the menu and only the menu off the table, but in the following shot he has one of the blue paper towels underneath it. (00:27:30)
Episode #3.4 - S3-E4
Continuity mistake: When Catherine brings the casserole of deadly confit de poulet, Humph unfolds the paper towel in the first shot but it's still perfectly folded in the next. (00:28:10)
Episode #3.4 - S3-E4
Continuity mistake: Dwayne is reading the local newspaper when Camille and Humph get back from the hotel. The paper folds in opposite directions in the two separate shots. (00:36:40)
Episode #3.4 - S3-E4
Continuity mistake: The hands on the close-up of the phone record sheet are inconsistent with the wider angle (Goodman's left hand should be in frame). (00:37:10)
Episode #3.4 - S3-E4
Continuity mistake: When Goodman crawls to get the poison vial, it contains just a bit of liquid left at the bottom. Later when he checks it out at the station in greater detail and many close-ups, it's over half full. (00:40:40)
Episode #3.4 - S3-E4
Continuity mistake: During the denouement, Helen Walker's hair goes from still to windblown and back suddenly between cuts multiple times. (00:45:00)
Episode #3.4 - S3-E4
Continuity mistake: In the final part of the enquiry, Goodman pulls out of the evidence bag with the bottle of poison; the bag is turned differently between shots (check out of the small ribbed part in the corner, the bottle's cork). (00:45:40)
Episode #3.4 - S3-E4
Continuity mistake: Simone's reaction shot to Helen saying "I wasn't even here!" is flipped, as the position of her hair makes obvious (she wears the hair combed on the opposite side throughout the whole episode). (00:47:05)
Episode #3.5 - S3-E5
Continuity mistake: Inspecting the study where the victim supposedly killed himself, DI Humphrey Goodman at one point rattles the window handle and then at the cut stands side by side with Commissioner Selwyn Patterson. In the shot from that particular angle, which repeats itself a few seconds later when he says it's "one of those things" after he made an exaggerated shooting gesture, his right hand does not appear gloved (and he tucks it both times rather quickly under the other arm), while he wears latex gloves in the rest of the scene. (00:05:20)
Episode #3.5 - S3-E5
Continuity mistake: The two detectives plus the Commissioner have broken to the family the news of the case being a murder investigation. They walk down some stairs discussing the case; Dwayne' scooter is visible in the background, shadows in its vicinity. When Patterson bids his farewell, Camille and Humph get called by Dwayne; the shadows by the bike now extend through a larger space all of a sudden. (00:09:05)
Episode #3.5 - S3-E5
Continuity mistake: Camille tells Humph that Marlon Croft they just spoke to is "probably" her father. He reaches them outside; during the scene the passersby walk at relaxed pace yet the street crowd behind Marlon completely changes after the brief cut on Humph and Camille. (00:13:30)
Episode #3.5 - S3-E5
Continuity mistake: When Camille tells her mom about Marlon being on the island, she turns around theatrically asking back "Your father?" Throughout the scene, Elizabeth Bourgine's arm position and stance appears subtly inconsistent between shots, and Camille goes from having one hand at the hip to the arm flat against her side at the cut following "It's just bad luck." (00:14:10)
Episode #3.5 - S3-E5
Continuity mistake: There is a cut when Humphrey says "if you caught your dad having an affair..." Camille's bottle of fictional beer is then facing a different direction. (00:19:25)
Episode #3.5 - S3-E5
Continuity mistake: After checking the phone records, the detectives go talk to Drew. Throughout the scene he has his left arm perched on the back of the seat, or just down his side casually. (00:23:00)
Episode #3.5 - S3-E5
Continuity mistake: Showing it to the police for the first time, Marlon is holding the plane ticket in his left hand when the camera is behind him, the right hand in the frontal view. (00:29:05)
Episode #3.5 - S3-E5
Continuity mistake: The reconciled Camille and Catherine walk arm in arm towards the table with Dwayne and the others. The beers in the bucket in front of Humphrey change position/angle depending on the view. (00:50:40)
Episode #3.5 - S3-E5
Continuity mistake: When driving to the crime scene, the vehicles seen in the wing mirror are constantly appearing and disappearing instantly.
Episode #3.5 - S3-E5
Continuity mistake: The land rover is going on a track but the next shot inside shows a road in the side mirror's reflection.
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.
raywest ★