Malphite passivle/Warmog's passive bug

When playing Malphite on HA, I built Warmog's and had over 3000 health to activate the Warmog's Heart passive. However, if damage has only been sustained on Malphite's shield passive, but not his health, the icon for Warmog's doesn't display a cooldown on the regeneration passive, and bonus regen is not granted.

So in essence, either the icon for Warmog's is bugged when shield-only damage is taken, or Warmog's is not granting health regen when shield-only damage is taken. I imagine the former is true, though.