Illusion/Dark controller, Superior Invise and Shadow Fall not stacking defense

[Outrider_01]

Im pretty sure its intentional but can someone confirm that a primary/secondary of Superior Invise and Shadow Fall are not supposed to stack the defense?  It seems odd, as Shadow Fall gives the give 5.78% def and Sup Inv gives 5.22% until combat which cuts it in half to 2.61% . Shadow fall is slotted for defense, Sup Invise is just a mule for LoTG but comes in handy as an invise power.