Hammer Throw Passive "Mana Starved Forging"

I noticed when leveling up a new Paladin with hammer throw, this passive is suppose to allow you to keep throwing the hammer even if you have zero mana. However; I noticed that when the mana cost would go below zero, he just won’t cast anymore. I have to wait until his mana comes back to zero before it will cast again.

I have the same problem its annoying

I have the same problem. kinda ruins the skill… when you have to w8 to recast it