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)
Continuity mistake: Magnum threatens to leave, but Adelaide sulks hard enough to keep him on the case. When the camera is on her, the Detroit Tigers cap is reflected in the rear mirror, and it keeps the same position regardless of Tom Selleck's head movements in the other shots. (00:09:15)
