Reduced mana support gem bug

The reduced mana support gem doesnt benefit from quality.
Even though the tooltip changes to up to 10% increased mana reduction, the actual effect of the support gem doesnt change.
I have two identical reduced mana support gems regarding their level, one with 20% quality and one without. Both reduce the mana cost for my auras by the same amount.

Auras don't benefit from the "Reduced mana cost", at least that's my understanding of it. Other skills are affected by the quality, no idea if it's a bug or not.
Reduces cost of skills from passives don't affect auras so it MIGHT be intentional, but I can't know for sure.

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Vipermagi wrote:

The Quality bonus does work, but Auras are exempt; they don't have a Mana Cost, but a Reservation. Reduced Mana Cost passives also do not work on Auras.
As is often the case, the Skill Gem discussion threads have relevant information: http://www.pathofexile.com/forum/view-thread/13808/page/2#p514550. :)

Thank you for that.