Raiment of Eyes robe not granting matching eye spells consistently

[XUV8R]

I have an allied Slimy Spore Beast which obviously has the Slime tag. My Eye of Blood spell, which has the additional Slime tag from the "Eye of Plasmoid" upgrade, is not granted to this ally. It is being properly granted to the slimes spawned by this ally, so it's not clear what the exact issue is.