The Case of the Red-Faced Thespian - S4-E12
Revealing mistake: Magnum arrives at the Nest. He opens the door and moves past two swashbucklers to talk with the person playing the piano. Is he really playing the piano, though? Apparently not, because the instrument is open and you can see that the inside does not move at all. (00:07:00)
The Case of the Red-Faced Thespian - S4-E12
Revealing mistake: When Magnum and friends are trying to figure out of the invitations mystery, the telephones on Higgins' desk are unplugged. (00:36:00)
The Case of the Red-Faced Thespian - S4-E12
Other mistake: In the opening credits, the title of the episode appears without hyphen. (00:01:35)
The Case of the Red-Faced Thespian - S4-E12
Plot hole: The plot of the episode has a big reveal that tricks the viewer making zero sense; the victim is alive and well, but there's an ambulance, they bring the victim away, and Magnum spends most of the episode in the noble effort of saving Higgins from a murder accusation. Magnum mentions "I figured I still had about a half an hour before Tanaka returned with a warrant for Higgins' arrest." even in his internal monologue, so it's not that he was trying to hide the fact from other characters.
The Case of the Red-Faced Thespian - S4-E12
Continuity mistake: Trying to exterminate the mongooses with extreme prejudice, Higgins lights up the bombs twice in two separate shots. (00:03:35)
The Case of the Red-Faced Thespian - S4-E12
Continuity mistake: Higgins mentions Robin's project to finance "a home for incorrigible boys." He already has in hand the two bombs he reaches for in the bag during the next shot. (00:03:10)