Punctured Lung notable passive doesn't work as advertised

The notable passive says:

> Enemies you fully armor break cannot Regenerate Life
> Enemies you Fully Armor Break are Maimed

I fully armor broke a horrible Shade Walker abyss boss that had Regenerate Life, and he kept happily regenerating life.

After fully armor breaking the thing a bunch of times while fighting it, the passive kicked in and I killed it easily. Unclear if the bug is it not firing all the time, or the UI erroneously reporting full armor break, or some mechanic that is not explained.

edit, more details: Playing solo, in a map. My manifested weapon also breaks armor. I wonder if the passive doesn't fire when the companion is breaking armor, too?