Reduced Mana Cost Exploit

I found out that if you use Reduced Mana Cost on a buff skill and swap out either of the gems and link RMC to another buff in a separate link then the old buff reserves mana the same as if it had RMC linked to it still. This can be used to reduce the mana cost of auras/buffs without having all of them linked to RMC at once, which in my case, allowed me to use 1 more buff than I would have otherwise been allowed. I'm not sure if this should work like this, but it seems like it shouldn't to me.