Titan's ascendancy "Ancestral Empowerment" doesn't work on Forge Hammer

Ancestral Empowerment is supposed to make each second slam skill ancestrally boosted, but for some reason it doesn't seem work on Forge Hammer. Perhaps I misunderstand something. For example icon and ability animation changes on Earthquake each second time I use it. But on Forge Hammer nor icon nor animation ever changes. But animation and icon do change if you use Fist of War support gem. So it' seems to be a bug.