Bahamet boss is bugged?

Zumsic

He is regenerating beyond phase threshold so it is making it impossible to take him down. It clearly states he shouldn`t be able to recover health beyond that threshold. Is that a bug or?
You can see in the picture it says Phase 4, but he is at 11% at that is rising through fight.

Darkraw346

True, if you're in the fight and he regenerates past a phase threshold it's fine, but if u lose the fight and enters again, he then enters the phase that matches his hp, even tho you've already got through that phase