Ngamahu's Flame + Ancestral Warchief broken?

I was pretty excited when I saw the new Ngamahu's Flame unique item, and started theory crafting a Chieftain/Warchief build around it. So far it's pretty fun with nice damage and good defenses from the chieftain ascendancy. However, why doesn't the Warchief trigger Molten Burst from Ngamahu's Flame? The wording on the axe states "on melee hit" and since Warchief uses your weapon AND is a melee hit then it should work right? Kind of a let down, was hoping to get a bit more DPS out of Warchief since it got a nerf, and it would be awesome to see him spewing some molten rocks on enemies heads!

Ah, that's a bummer. This is my first totem build so wasn't sure if there were restrictions on totems triggering such effects. Kinda sucks that Cyclone is all this axe is good for right now.