I'm assuming this is a bug. If I have both Duality of Mortal Presence and Cautious Attack active, then disable DoMP, then CA, then reactivate CA, then DoMP, in that exact order only, the deflection bonuses stack. DoMP shows up as suppressed in the character sheet but the bonus is still reflected in the total deflection score and in combat.

 

It would actually be nice if they stacked as that lets you build monks for tanking  a little better without having to throw them in heavy armor. It also makes cautious attack pointless if they don't stack and you also have DoMP.

Huh, I encountered this as well, but I was thinking it was intended behaviour since I didn't care to change the order of activation around.

Anyway it's inconsistent since there should only one modal be active at the same time.