Bug with the Life Mastery "15% increased max life if no life modifiers on equipped body armour" ?

So I was experimenting with different armor types and noticed that a particular piece of armor that had a life modifier on it did not decrease my max life when equipped, even though I have allocated the Life Mastery "15% increased max life if no life modifiers on equipped body armor".

When Equipping other armors that have life modifiers, the mastery works as intended and decreases my overall life by the 15%, but with this one particular piece of armor my health value remains unchanged. I have tested a few other armor pieces with life mods that I had in my stash and the mastery worked as intended; it seems to just be this one particular Majestic Plate...

Below are some screenshots illustrating the issue.

1. Showing I have the mastery allocated:



2. With the bugged armor equipped:



3. Same total life value as when armor has no life mods:



4. But mastery is working as intended for a different piece of armor:



Another example of the mastery working as intended:



6. Screenshot with no armor on, just in case:



Is this a bug or am I missing something fundamental about the mastery or the armor mods here?

Ahhh that makes sense, I thought I was going crazy lol. Thanks for the reply.