No effect from Ioun Stone?

So I purchased a +2 int ioun stone from a vendor (Scarlet and Blue Sphere) and...it doesn't seem to do anything. I believe I am activating it correctly (through the PC Crystal) and while the animation does appear, my stats are not affected. I am certain I am using it correctly, as I also have a +2 Dex stone and that one activates and adjusts my stats as it is supposed to. And no, I am not at the +12 ability cap for intellect. My only source is a +4 off a helmet (+6 if the stone were to work).

Is there something I am missing regarding the int one? A level requirement to use or something? I don't see anything in its description. Or is this a bug?

Helmets (the ones that turn into "bands" and auto-unequip themselves) do not stack with ioun stones.

Ah that would explain it. Thanks for the response!