that's bizarre! the whole idea of humbucking is independent of the magnets and pole pieces. one coil picks up random RF interference... and the other one picks up the same thing in reverse phase. when they're put together, those two opposite signals cancel out. the poles and magnets have nothing to do with it. I'd love to know how that happened! I've done this 6-7 times on multiple brands of pickups and always had full hum cancellation.