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)
Other mistake: Twice in the episode it is explicitly said that Magnum's phone has been disconnected, and that Higgins checked with the phone company. Yet at the end, it turns out 'the lads' chewed on the cable. Surely the phone company wouldn't tell the estate manager that the line has been disconnected for billing problems (so, a well determined administrative issue with proper paperwork done) when it's a wiring problem.
Other mistake: Lee has an Atari 830 Acoustic Modem, which has on its front panel an instructional "cord side" illustration, showing the proper direction for the phone cord when the phone handset is secured in the top two cups. The telephone's cord must be placed at the right side in order for the acoustic coupler to work, but in both Lee's and Magnum's closeups, the phone cord is on the left side, but the acoustic coupler works properly. This is impossible. Also noticeable in closeups is the covered brand name of Atari on Lee's devices. (00:24:20 - 00:27:20)
Other mistake: With episode 11, "Thicker Than Blood", the opening changes to the truly iconic version associated with the series, with a large overhaul of footage. There must have been some hiccup making it though, because the title of the series appears as "Magnum PI", no punctuation. There's a version of the opening that includes the correct "P.I." title card.
Other mistake: The three friends mistake Higgins' footprints in the sand for a pirate's. They find him and they have their explanation; Higgins is carrying a cane and some palm leaves; dragging the palm leaves, he involuntarily erases the prints of his foot, while the cane leaves a circular print akin a wooden leg's. That makes no sense, because as it is shown, Higgins is holding the cane in his right hand, and dragging the palms with his left; he'd wipe the prints of his left foot, if anything. And yet when Rick pointed at the prints, it was obviously a left footprint. (00:18:20)
Other mistake: Rick enters Wendy's room shouting like a madman, and then reaches the bedroom door trying to turn and pull the knob. He bangs the door, calls for Magnum's help, and both then bust the door open. In all that, the guy going through Wendy's underwear and bed sheets is still unfazed and stops what he's doing merely when they almost fall on him. (00:18:00)
Other mistake: Magnum wakes up because Agatha and Higgins are playing with their model planes that loudly buzz in the air. He opens his bedroom window and here they are, by the guesthouse, with a direct view and Higgins waving at him. He then gets out to give them a verbal beating, and he's coming from the main house area. (00:02:15)
Other mistake: Higgins is outraged about a precious 1923 sketch being stolen by Rick's friend. Then again, that invaluable (as he puts it) piece of paper was stored in an open rack, rolled up with a rubber band. That's hardly how such an antiquity would be preserved by someone who finds it this valuable.
Other mistake: The guy rummaging through Waldo's stuff in the room does not get alerted by their loud chat outside the room, nor the door unlocking, not even their steps; he just turns around suddenly when they both are in the room, standing still in silence and looking at him, who has his back turned to them. Must have had eyes on the back of his head. (00:09:10)
Other mistake: The guesthouse scene with Magnum and Luther opens with a prolonged gag about Magnum "finally" getting an answering machine. It is said that it's the first time he gets one. But in the season 1 finale, "Beauty Knows No Pain", Magnum's client Barbara Terranova commented that the message on Magnum's answering machine mentioned the club. (00:03:25 - 00:18:00)