Edit: Confirmed!! Armor piercing (at least on the Envenomed Blade) applies armor piercing to both weapons equipped! Let me know if you want a screenshot.
So I pulled the Envenomed Blade today. Sweet weapon, tons of fun all around.
"Armor-Piercing - 10%: If the Target of this weapon has ortification, it will be trated as having 10% less Fortification..."
I always assumed this meant it only applied to the Envenomed Blade. However, this is what I'm confused by. When you equip the weapon, it shows up in the combat log.
(Combat) You Benefit from your armor-piercing -10%.
(Combat) Bypasses 10% enemy fortification
This seems to denote the effect is more of a global one. To further illustrate, equipping a Disease Immunity item will pull up a similar message in the combat log; (Combat) You benefit from your disease ward.
So with those considerations in mind, does Armor-Piercing only apply to the weapon the effect is on or does it apply to both weapons much like Sneak Attack does?
*If anyone has done testing on this, I would LOVE to see those results*