Draining Energy Shield to 0 still avoids stun with Skyforth/Blood Magic

I have tested this interaction in game. I am running Skyforth with Blood Magic, so my stun threshold should be 0 and every hit should stun me. Having any energy shield provides a 50% chance to avoid stun. However, even after draining the ES to 0 (with Blood Rage), I still have that 50% chance to avoid stuns. This goes away if I allocate Eldritch Battery. Normally, outside of Skyforth/Blood Magic, having 0 ES removes that inherent 50% chance to stun, so this current implementation feels inconsistent and unintended.