Armor spec cannot increase Thick Skin if both are applied at the same time.
Not a bug. Please submit a bug report so you'll run silent on the matter until they come back to tell you it's not a bug, it's simple mathematics.
Are you purposely being obtuse, or it just happening naturally? Because I'm using simple English and yet it's still doesn't seem to be clicking with you.
It's pretty clear from the math that things are being done additively instead of multiplicatively. That said, the skill could use an updated description just to make that a little more clear.
Thank you. Someone gets it.
