EU and passive Def. bonus

I'm trying to use EU as a base skill for a similar skill, "Equipment Upgrade", which among other things increases the Hero's defense. I have replaced the four levels of Demolish skill with four levels of "Equipment" skill that I made by modifying the base skill Devotion Aura.

My problem is that when EU is leveled up, it replaces every part of the old Equipment skill EXCEPT for the defense bonus . The Equipment skills each have their own custom buffs and UI icons (though they are passive) which are replaced, but the defense bonus simply doubles and then recedes to its original value. Oddly enough, if the buffs are the same then the defense bonus does not change.

Essentially my question is this: What do I have to do in order for EU to upgrade a passive defense bonus?

MD