Revealing mistake: In the night shootout, Magnum cocks his pistol in a close-up that is obvious performed by a trained stunt double. Whoever is doing this is wearing the same clothes Magnum has but with the T-shirt in pristine condition straight from the washing machine, while Tom Selleck just took a dive in the dirt. Moreover, he wears the team ring upside-down. (00:22:50)
Character mistake: The day of the race, Higgins reacts to Adelaide mentioning Norman as if it were the first time he ever heard the name, but he was present when she mentioned him, and the case. Not being all that involved, technically he didn't have to remember that, but he remembered the detail of the uncle, and forgetting that the woman was talking about someone being murdered, is quite odd - and is just done for the cheap gag that follows.
Revealing mistake: When the bandit holds Adelaide and then drops her off the horse, you can get a good look at the face of the person, and it's a younger stuntwoman, not Christine Belford. That stuntwoman has to roll in the dirt and get up, but Christine Belford emerges in the next shot without a speck of dirt on her shirt's sleeves nor the back of the jeans that got all soiled earlier. (00:14:45)
Continuity mistake: Inside Higgins' study you can get a great look at Magnum's dirty shoes when he sits with his feet up on the desk. Those shoes have a blue logo on the tongue. Later there's a close-up of Magnum and Adelaide's feet when Magnum drops the gun in the stable, and the shoes are very similar but different, lacking the blue logo. (00:39:15 - 00:44:15)
Continuity mistake: Rick and TC their back to Magnum and scoff at him. Magnum chases his primadonna friends to convince them to help him. During this scene, the same rider approaches the gate, accompanied by a stable worker with a baseball cap that is first red, then yellow. (00:29:10)
Continuity mistake: Magnum before the race tells Adelaide to "Ride like the champion you are." Behind her, a woman with a beige hat with a leather band walks by, along a man with curly blonde hair. Same two pass her by, again from the same direction, in the next shot several seconds later, and again another few seconds later when he tells her to smile. (00:27:15)
Continuity mistake: Higgins and Magnum bicker quite a bit about Robin Masters' box, the horse client and rugged chukkers. During the whole scene, the same extras walk back and forth repeatedly with no logic. For instance, the woman in blue shirt and a straw hat, popping up behind Higgins first and then behind Magnum in the opposite direction when Higgins asks "Another uncle?" (00:25:30)
Continuity mistake: Magnum shoots at the bad guys who flee after setting on fire the stable of the rival. In close-up, Tom Selleck acts a bit, with an expression of disappointment at missing them and some energetic gesture. None of which happens in the longshot, where he repeats the same action but with no such flair. (00:23:00)
Continuity mistake: The baddie is a real sharpshooter and punctures the tire of the jeep with a single gunshot. The jeep's wheel stops its spin in a close-up, but when Magnum gets off the jeep the tire looks fine, and it stopped in a different position - as you can tell by the position of the brand logo. (00:14:50)
