I think the backstab skill is bugged, to be specific，the Apprentice training. In its description，it says " a successful rear attack upon an unaware opponent will bypass his armor ",but that is not true,you donnot get to bypass your unaware foe's armor at all!!!!!!! Try it yourself, just get your follower's DR up to 95 and then stab him in all possible way then you will see. I donnot know why did not any body notice it before,maybe because backstabing an unaware opponent will gain an additional 100 damage when you have 5 cp put in backstab, the huge damage may let one think he has bypassed the enemy's armor, but he didn't, btw this bonus doesn't need any training. I'm playing the latest UAP of course.