Vagabond AC Bonus Reduced by DEX Buffs

[Lira]

I play Rauva T'kar, a Vagabond-perk fighter. Earlier today another PC buffed me with Cat's Grace, taking my DEX from 14 to 16. I promptly lost 2 AC net, or 3 AC total counting the increase from the higher DEX. That's equal to my Vagabond AC bonus in my leather armor.

I know from past experimentation that having 16 DEX naturally on a Vagabond will reduce or disable your bonus in leather, but I was under the impression that magically-applied bonuses wouldn't cause this.