Mana drain from reserved max health

Pretty sure this isn't what was intended but could be wrong. I'm playing Infernalist and have just taken Beidat's will trait. After taking this my mana is constantly draining to 0 which confused the hell out of me. After a bit of looking I've found that my chest piece The Black Doubt Hexer's Robe has a modifier 'While not on full life, Sacrifice 10% of mana per second to recover that much life'. The way I am looking at the reserved life personally is '25% of your health is no longer accessible so your maximum health is 75% of what it is supposed to be' But it is acting like I have lost 25% of my health which is activating the trait to drain my mana and restore health that isn't technically missing?

I'm in the same boat as you.
I'm wearing 'The Black Doubt' hexers robe with the same modifier, I'm permanently bingo on mana.
I don't think this should be this way.