I can't help but think this is a bug or at least unintentional. Compared to weapons, which only activate passive bonuses if you have them equipped (and even activate them twice if you dual wield the same weapon!), this seems really odd. For example, I have Shield Bearer, and am Dual Wielding Peasant Pitchforks right now, and because I doubled the bonus from Sensible Swiss Defensive Stance and still retain the bonus from Squire of the Shield, I have 31 block rate at level 3. What is interesting is that even if I equip a shield instead of one of the Peasant Pitchforks, all that changes is I lose a bunch of damage. My block rate remains unchanged because the passives from the Polearm line added up to 3 block rating per Polearm equipped, which is what the starting Wooden Shield gives you. Granted, this is the most Block you can get from Polearms, but it illustrates my point. Dual Wielding the same weapon and taking the Shield Bearer line gives no penalty to either. This has bothered me since DoD was released :/ On a related note I'm pretty sure all of the Master of Arms skills work without wearing heavy armor as well. What would be really nice is if one of the later skills in that line reduced some of the penalties you get for wearing heavy armor (only when actually wearing heavy armor).
By the way, dagger skills seem to behave the same way. At least I'm able to perform an extra daggery attack (Liechtenauer's Switcheroo) with a staff
