Visible crew/equipment: By the car exit of the Mokihana, both in coach Lum's car and in the Ferrari you can see the reflection of people standing by to film the scene. (00:44:10)
Continuity mistake: Magnum comes back to the beach after some surf ski, where the prince struck a 'deal' with Ed Russler. Magnum's shirt is wet in two completely, and that's not a understatement, COMPLETELY different ways before and after John Saxon approaches. (00:28:30)
Visible crew/equipment: Inside Benny's glasses when he is taken back to the Estate is the reflection of the set light screen. (00:39:10)
Continuity mistake: Rick tells (and shows!) Magnum that he's writing "a recipe for Veal Marsala for my mother back in Chicago." But the key plot element of 4-4 "Distant Relative" was that Rick raised his sister by himself, because Chicago was "a tough town to grow up in without any parents."
Other mistake: Fun gag but does not make sense; Magnum has a prolonged conversation at the bar (not a random brief chance encounter) with Lou Whitaker and Alan Trammel, and he, a huge Tigers Fan who in other episodes proved to be able to recognize obscure players from other past teams, needs the bartender to tell him who they were. (00:27:30)
Continuity mistake: Magnum and TC are talking at the beginning of the episode, by Rick and his peachy polo. Magnum has always his hands on his hips in TC's close-ups and in front of his belly in the wider angle shots. (00:02:15)
Other mistake: Finally the gang is set free; the policeman says "Your bail arrived." Magnum asks "Carol Douglas?" But Carol's last name is Baldwin in the other episodes she's involved in. (00:35:30)
Continuity mistake: Magnum and TC hi-5 at the beginning of the episode. The football bounces at distance from TC in the first shot, but it's right at his feet after their hands clapped. (00:02:00)
Continuity mistake: Magnum is bullied into going with Carol's lame plan. The very first shot of him and TC on the Ferrari on their way to block the drug lord shows TC wearing a white sweatband on his head he does not have in the rest of the episode; it's recycled from 1-13, All Roads Lead to Floyd, and you can even spot the car typical of that episode. (00:29:10)
Continuity mistake: Magnum begins to open the safe; the sensor with the red wire is in left position, black wire in right position. When he removes the sensors, it's the other way around. (00:23:00)
Continuity mistake: Drunk Carol is telling Magnum why she was fired. As she says "They took it away from me", her hand is in front of Magnum's, and yet it is on top of it at the cut. (00:06:00)
Revealing mistake: TC runs into Higgins avoiding him in the front view with John Hillerman, and hitting him when he's replaced by a stuntman. He also is sprawled face down on the lawn with one or both arms up. (00:02:45)
The Case of the Red-Faced Thespian - S4-E12
Plot hole: Magnum mentions that he spoke "one hour ago" to Robin, getting the description of Lowell Xavier Jameson. All the suspects are at the estate, and Tanaka arrived, apparently with an arrest warrant for Higgins, when Magnum still hadn't spoken with Robin. Magnum did have to bargain for Tanaka to put off the operations by two hours; it does not make sense that he'd be around at the estate one 1 full hour more for unexplained reasons.
The Case of the Red-Faced Thespian - S4-E12
Revealing mistake: In the climax of the episode, Magnum tackles Higgins to the ground - but it's an obvious stunt double. (00:45:10)
The Case of the Red-Faced Thespian - S4-E12
Other mistake: As said in the ending, Lady Cynthia Warrington-Stout was on Higgins' bed when she was found; the room looks nothing like Higgins' room as shown in Foiled Again (3-8).
The Case of the Red-Faced Thespian - S4-E12
Continuity mistake: Magnum puts the register on the armchair while Higgins is looking at the invitations. He pulls away, but in the next shot he's still hunched over the armchair. (00:36:40)
The Case of the Red-Faced Thespian - S4-E12
Continuity mistake: Higgins, back in his wits, walks into the studio while Magnum is brainstorming with TC and Rick. He spots the invitations and examines them; as he approaches them you can see they are spread out in a fan, while at the beginning of the scene they were stacked in a neat pile. (00:36:15)
The Case of the Red-Faced Thespian - S4-E12
Character mistake: Magnum quotes in his mind (right after the $20,000 turns up in Higgins' room) and then out loud (during the denouement) that "Old wounds heal slowly." The quote is from a movie he watched earlier...but it said "DEEP wounds heal better slowly." (00:30:55 - 00:35:40)