Summon Sacred Wisp Gaining Mana Cost From Reflected Mod

I'm uncertain whether this is intended or a bug..
It appears that the reflected crafted accessory mod "Non-Channelling Skills Cost +X Mana" (originally "Non-Channelling Skills Have XX to Total Mana Cost") adds a mana cost to Sacred Wisps Support whenever the supported skill hits a target (which triggers Summon Sacred Wisp).
Observation: Mana gets depleted when Kinetic Blast supported by Sacred Wisp Support hits a pack of enemies. There's no mana loss when the support gem is removed.