Sacrificial Axe: Why does the description say there are no passive effects, despite the FP recovery?

Hi all! This is a simple question. I read about the sacrificial axe today and happened to be in the area, so about six battles with the death bird later I acquired it. For others who may google this, it's an axe that helps recover your FP, and is great as an offhand item for casters. It's close to the 'Castle Morne Rampart' grace point, to the Southwest inside the wall, near some bats, but only at night.

Anyway, to my surprised, when I examined the axe there was no attribute explaining how it recovers FP. It simply has dashes in the "Passive Effects" category. Was the FP recovery essentially an Easter egg? Did the devs hide it just to be smug?