escape artist and defense bonus?

I'm not sure I'm reading the in-game info and wiki right:
With Escape Artist specced, I purchase the Evasion mastery "100% increase to Evasion Rating from Equipped Body Armour", and my ES rating is unchanged.
Do I understand correctly that this mastery does not raise the evasion rating of my body armour, but that it only calculates the evasion of my body armour into my total?
Or is this interaction (EA and Evas mastery) bugged?
thank you