Omen of the Leige

How do i even make this work? I have it active in my inventory. I go to apply the Armor-type Preserved Rib to literally any armor type (un-desecrated) and i keep getting a Incompatible Desecrate item error.

The wording is exactly the same as the Prefix/Suffix omens that work just fine.

It appears to work fine on a Weapon, but not on any armor types.