Revealing mistake: When Humphrey checks out of the mail from the dating website at the end of the episode, behind the window of the mail client, there's a fingerprint file with the name "Adam Frost" and a 2014 sampling date; it's a file recycled from two seasons before, 3-4. (00:49:55)
Plot hole: The whole plan for the murderer to create a perfect alibi hinges on an incredibly precise timing of the victim's action and bodily reaction to the poison, both out of his control. The Governor needed to shake a lot of hands and deliver a speech without yet dropping dead, and everyone needed to ignore entirely the signs that she was feeling unwell. In fact, she needed to collapse as she was drinking, dropping the glass and doing it somewhere where he could squirt some more of that poison in the glass. He couldn't predict the whole situation with the glasses and the Commissioner that would create the alibi (he leaves the party when refreshments are just being served), but for this unpredictable chance to get an alibi he took the huge risk to carry the whole bottle of poison with him, which the plot never explains why was never found by the police or disposed of.
Continuity mistake: In the intro, Zoe appears all of a sudden by the stage entrance; the other two models were on the runway with nobody there before the cut. (00:00:15)
Continuity mistake: Sadie Mernier tells the police about the victim's stalker. In close-ups, her large hoop earring is caught between her hand and her face. Camera further back, and the earring is on the outside. (00:09:35)
Continuity mistake: When Humphrey turns towards Florence to mutter instructions about checking the case with the UK police, Joséphine Jobert's hand is positioned on the top side of the notepad, and in a different position at the cut. (00:09:50)
Continuity mistake: Humphrey and Florence are checking out of the crime scene the morning after. When Florence says "Also, if she's telling the truth" the pen did a 180° turn in her hand; it had the ballpoint up, now it has the cap. (00:10:45)
Continuity mistake: Rosey Fabrice visits the police station the morning after the murder. Dwayne puts his moves on her and places his hand on the back of her chair, but in the close-ups his arm and hand are simply not there. (00:12:10)
Continuity mistake: DI Humphrey Goodman writes the name of the victim on the whiteboard, in a close-up. He then starts enumerating the suspects, but the name changed penmanship - look at the odd shape of the E linked to the previous letter, or the suddenly shallow M. (00:13:50)
Other mistake: Florence closes her notepad and puts the cap back on the pen when Dwayne just begun telling everyone what the Gendarmerie reported about one of the suspects. She has no way to know by that point what Dwayne is about to disclose, and that Humphrey is about to leave with her. (00:17:05)
Continuity mistake: Florence walks towards Goodman reading the post-mortem results; before the cut, you can see Kris Marshall's chin leaning on his right hand, but he has the opposite hand up and the right one down when he comments on the 'small mercies'. (00:23:20)
Continuity mistake: Florence advises Humphrey to "just be yourself." The slice of lemon is on (her) left side of the glass. Reverse shot and it's the right side, then it is back on the left side, where it remains for the rest of the scene. (00:28:35)
Continuity mistake: Humphrey sat down with the photographer, and asks him about the incident that bankrupted his previous agency. He says "Of course I would", scowling and putting the right hand on his left arm. Reverse shot, and his hand is on his knee. (00:34:05)
Continuity mistake: In an uncharacteristic display of authority, Humphrey orders Sadie Mernier to go back to her chair and answer the rather personal questions. She walks back with her shades in her right hand, and in the shot when she slumps back in the chair, the sunglasses are in the left. (00:37:10)
Continuity mistake: When Humphrey sits at the killer's table, they have the right hand on the left elbow in the first shot, both arms forward in the next. (00:45:55)
Continuity mistake: Dwayne's bottle of Etensel is facing opposite directions when he tries to act as if he didn't see his boss embarrass himself at the bar; the label faces the camera when the camera is to his right, and to his left. (00:50:35)
Continuity mistake: After the mishap at the bar counter, Humphrey reunites with Dwayne and Florence. He puts the glass on the table when he sits down, but in the next shot he's still holding it and only after a while he puts it back down. (00:50:40)
Continuity mistake: At the end of the episode, Catherine hands Humphrey the rag held in two different ways in the separate shots. (00:50:45)
Continuity mistake: At the end of the ceremony, Dwayne and the other friends of the deceased are walking out of the church. The woman with the golden hat in the background changes position, shaking hands next to the closed window, but moving close to it only in a later shot, as she is still seen walking out of the open door when Dwayne steps down after taking a sip in memory of Cedrik. (00:01:15)
Continuity mistake: Dwayne takes a sip from the flask at the exit of the church. When he gives it to the priest, his friend has both hands on the fence, but at the cut he's wiping his eyes with the left hand, only the right hand is on the picket. (00:01:30)
Continuity mistake: Dwayne and Humphrey take a walk from the sidecar to Cedrik Verga's house. The shadows on the road differ between shots - easy to notice looking at the parking markings. (00:06:30)
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 ★