Soul Thief Support Gem bugged

So I have 5.77% mana leech on my gloves. When I open up any skill you can read it it on On Hit Effect.

When I equip the Soul Thief support gem into the skill, the on hit effect totally disappears in the tooltip. So its not like it just doesn't show form the gem, the effect which was already shown from the gloves disappears.

I want to use it on Ice strike but I just tested on all my attacks - same thing.

So its at least a tooltip bug but I am pretty sure it also doesnt work at all as I have instant leech, and no mana is instant leeching.

This is still broken.

My mana theft shows as 65.54% whether I have the gem equipped or not, and that's the amount of general leech I have.