This has me thinking about the effects if the 2 coils are wired incorrectly, or the other options.
I'm thinking if one coil start and finish are reversed, it may cancel the hum bucking effect.
I think I recall if you want the out of phase / Peter Green deal, the magnet needs to be turned to be out of phase with the other pickup.
I guess if you wire them parallel, the polarity has to be right / opposite to keep the humbucking effect.
I reckon all this can be found on the web, sorry for the rambling.
The Dimarzio PAF Pro I bought used sounded really weak when I first installed it - in the neck of my semi hollow.
It didnt hum like a single coil from what I remember, or it wasnt so loud I took note of it.
I wired it the way it came; one pair spliced, one lead with the shield, and the hot by itself.
Turns out it was wired wrong - I dont recall exactly but I think one coil was the spliced pair, so it was only operating as a single coil.
Anyway, sorted it using the Dimarzio wiring diagram - it sounds great.
PIA, but it gave me the practice and experience both troubleshooting the pickup and fishing the semi-hollow.