Impresence Mana-Reservation of Vulnerability

Hello,

the amulet stat says "Vulnerability has 100% reduced reservation if cast as an aura", but it sill costs 8 mana (level 1) for me to activate it with blashemy support.
Tried to understand it in PoB, but i dont ;)
https://pastebin.com/hYWeUKyY

As 100% is a quite absolut value... i assume this is a bug?

EDIT: depending on the order of activating the auras, i can just activate it, e.g.:
major auras, precision, vulnerability -> doesnt work
major auras, vulnerability, precision -> works

Best regards

not a bug, that is casting cost not reservation cost.

well i see, my bad ;D