Doryani's Delusion Sorc boots LvL 25 Purity of Lightning Bug?

Is there a bug with Doryani's Delusion boot aura's? So I sit at 44% lightning res before i turn on the aura. I turn on the aura and am still at 44% lightning res. It reserves the mana when i do this, it is worth noting i took off the old purity of lighting gem so the only one i could reserve would be from the boots.
I tested tested the gem again and sure enough go up to 85% again.
Is there something special i need to to do get the boots aura to function properly?
There isn't any circumstance where turning on a lvl 25 purity of lighting would have no effect on your lighting resistance. Little puzzled why it has no effect. Any help or clarification would be greatly appreciated.

Thanks from a first season newb :)