Claw mastery instant leech - bugged/zero effect

As title says, instant leech notable of claw mastery doesn't work. Might also be the case for life/mana leech, but this is much harder to confirm due to lgoh/mgoh effects

Noticed/confirmed it the following way:
My build uses both leech mastery and claw mastery with instant leech. Thinking 15% instaleech was a bit overkill for what I was doing at the time, I unspecced the leech mastery. I noticed my ES would be bottomed out even while fighting large packs of mobs, it took me a long time and many deaths to finally figure out what was going on. I was only getting the slow and steady trickle of normal ES leech, as soon as I took the 5% instant leech mastery my ES would shoot back up instantly when fighting packs.