Amulet FireFlower +level of all fire skills not working with minions

I bought a fireflower amulet, and the game shows my Infernal Hound and Skeletal Arsonist gaining the +4 skill levels but they don't have any actual effect. Even if I take my other +6 minion skills (sceptre and helmet) off, the +4 still shows but doesn't change minion health or damage.

+