This scale armor is obviously missing the pierce damage DT, when you swap it with another armor, it has none.

 

When you wear it directly, the pierce resistance is not applied also.

 

Bug solving :

You have to equip it once, then unequip it without releasing it (keep it drag), and put it back in the armor slot, only after this the pierce damage DT applies.

 

BUT

 

As soon as you close inventory screen, you loose the piercing resistance.

 

Obviously bugged

Edited April 6, 201510 yr by vahadar

On the community bug tracker: https://github.com/PoE-unofficial/Pillars-of-Eternity-bugtracker/issues/13

@vahadar, do you happen to have equipped any other item which grants Pierce DR bonus? (they suppress each other)

What is exactly in the combat log, no Pierce DR applied at all?

I'm asking because I tried to reproduce (1.0.3.0530, linux, GoG) and so far wasn't succesfull. Durance with Hirbel's Protective Skin was attacked by bow by another party member, and the combat log formula consistently shows 9.0 Pierce DR substraction, which is correct number. So if you are able provide more info, that would help a lot.