Purity of Lightning sceptre aura is giving support gem benefit without cost

I recently upgraded my sceptre from one with the malice aura to one with a purity of lightning aura.
I have 2 support gems socketed that cost spirit but give a benefit (clarity and the one that gives minion damage when not on full mana).
I noticed that when I equip and socket the gems in the malice sceptre, I correctly reserve x amount of spirit, but when I swap to the new sceptre, no spirit is being reserved.
According to the sceptre and minion tooltips, the benefits still apply, I simply don't pay a cost.
I'm not sure if I might be overlooking something here, but it looks like this is a bug.