Does the StD Shield Expertise stack? I know the Arcane Archer explicitly states that it doesn't (Eg if your AA gave you +5 and you had a +3 bow, you'd count it as a +5, not a +8) but no such caveat for the Stalwart Defender.

Shield Expertise: Shields and weapons you equip gain +[1/2/3] to their Enhancement bonus.
AP Cost: 1 Ranks: 3 Progression: 10 Requires: Armor Expertise