The Magician - S3-E4
Revealing mistake: When Oliver meets Thea at the Grind and Jot Cafe (Which looks unsurprisingly like CC Jitters) you can see the cups on the table are from CC Jitters. (00:20:50)
Revealing mistake: When the band in the nightclub performs the made up song "Mr. Music Man", the suave Mr. Stone, the musician Miss Fisher ends up dancing with, is doing one heck of an hilariously incompetent job at faking to play an instrument, basically playing air-banjo strumming about 3 inches above where the chords are, and wildly off tempo. In the closing bit of the song (as the singer sings "To sin") he even moves his hand at the side of the strings and not above them. (00:03:30)
Revealing mistake: It's a valiant effort, but the scenes of Sherlock & Irene in a London street are shot in New York. Not only is the architecture wrong but you can see a U.S. pedestrian crossing signal over Irene's shoulder. (00:16:15)