Rathpith / Sacrifice bug -- losing more than 10% life

Occasionally when I cast a spell with Rathpith equipped, I lose more than 10% life.


See video around 0:20 seconds in:

https://youtu.be/UiHPfuh_ZlQ


My hp drops to ~8596, instead of what it usually drops to (~10000 hp, which is 10% sacrifice from Rathpith).

bug report reference number: 3,375,551,640

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It's not the mastery or it would have been consistent each time casted in the video.
Doesn't appear to be Automation since there's animation for Withering Step or buff icon for Automation.

I assume Cast When Stunned didn't have an active skill in it since it is empty socket currently.. but that's my only running (and kinda weak) theory atm is it somehow triggers even without an active skill at the same time you were casting BV causing 20% life cost (plus whatever Blacksmith hit you for). Easily disproven doing the same test without CWS socketed and still triggering more than 10% life cost. Or just having the excess life cost triggered while in hideout and not being hit.

It might also involve getting stunned at the same time as Rathpith sacrifices life when I cast a spell. If I take off Valyrium, my hp doesn't seem to dip as low.