Near the 1hour 13 Minute mark, Box is waiting at the car for Thursday & his reflection in the passenger side review mirror shows him in a short sleeve shirt but when they showed Thursday approach him from the other direction he had his jacket on which of course was long sleeved. No, it's something different. He's seen smoking with what would be the same arm. It's either a reflection of a crew member, or some type of double exposure.
When Dr. Nicholson finds the note tucked in the book in the library, he screws it up and drops it in a full bin. When Morse finds it, the bin is apparently empty (or at least emptier) apart from the note.
When shown a letter by Mrs Teagarden, Morse says he can't read German. Yet in "Who Killed Harry Field", he is fluent in the language.