Whoa, whoa, don't rush to tell everyone that you've found a bug just yet ;) For the outfit’s buff to take effect, at least one piece of armor on your character must go into a damaged state. When this happens, the remaining durability bar in the inventory will turn red instead of green. Another red image will also appear next to the radar. 
If some part of the armor is destroyed completely, then your opponents begin to receive less damage.