Smith of Kitava Fire Spell on Hit

On boss fights, Fire Spell on Hit skill keeps draining my mana with combo of Shockwave Totem and Forge Hammer. Whenever the totem pulses and fissures from the hammer hits the boss. This does not happen on normal mobs. I did some tests with and without the Kitava's ascension. I do not think this is intentional and maybe a bug that was overlooked.

Did more tests. I guess the skill gem on the ascension just keeps casting. Reason for mana drain