Party hat quality modifier bugged?

[martinuzz]

I made a q96 party hat. It gives me +21 CHA.
My village mate made a q71 party hat. It gives him +26 CHA

How can a lower quality item give a bigger bonus?

EDIT: I am full barbarism, he isn't.
But.. I thought belief slider buffs were applied to base value, not to item buffs as well? It's not a percentage change to the buffed total. I tried removing my merchant rings, and merch robe. Still, the bonus added from the party hat stayed 21.

[DeadlyPencil]

did you put his hat on to see the +26 yourself

[martinuzz]

I did now. It gives me +18.
So, it seems, barbarism slider does affect party hat buff directly.