Revealing mistake: The photo from the high school years of Edwina and the candidate is a photoshop Frankenstein where you can see the face of the actress pasted on someone else's head. (00:24:50)
Revealing mistake: Humphrey and the team receive the decisive last clue from Saint Marie; on the Scotland Yard PC, in the inbox there are tons of emails marked as 'today' that come from places like the Guadeloupe lab and instead days old. (00:34:35)
Revealing mistake: The photo found by JP in the newspaper archive is photoshopped so badly that you can actually see the line where Julian Wadham's face has been pasted onto the sailor's head. (00:44:55)
Revealing mistake: Dwayne turns the volume of the computer in DI Jack Mooney's office; when we start hear him, the volume has gone up just a few notches, but it's already just as loud in the end as it is when Dwayne finishes to set it. (00:29:10)
The Secret of the Flame Tree - S6-E2
Revealing mistake: Florence shows to her boss a copy of the birth certificate of Lizzie Baptiste. It is signed "Overseas British Territory of Saint Marie", dates back to 1954 with a photostatic copy of the original typewritten entry, and her school certificate is also written in English. Saint Marie though, according to its fictional history, was part of France at the time, having been a British territory only for 30 years before Season 1 (set in 2011). (00:25:40)
The Secret of the Flame Tree - S6-E2
Revealing mistake: The sepia-toned memento that Florence spies on the wall of Chez Lulu is supposedly from 1969, certainly a photoshop horror from 2017, with the faces of the two siblings ghastly superimposed. (00:24:25)
The Secret of the Flame Tree - S6-E2
Revealing mistake: At Catherine's, Dwayne is reading a copy of The Saint Marie Times, announcing the new candidate for Mayor. The text used in the prop though, is obviously the same used in the prop for the first episode of the season - the article is all about Commissioner Patterson. (00:26:20)
Revealing mistake: When Dwayne holds the copy of the local newspaper with his goat comment making the headline, the text of the article repeats itself; you can see aligned in both columns the name of the commissioner accompanied by "pictured right." (00:23:15)
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.
raywest ★
As long as such changes aren't an obvious continuity mistake (e.g. changing multiple times during a day), one can just assume the change happened in-universe as well. Things do get broken or updated occasionally. It adds a bit of realism, in my opinion.