Decaying Hex - Not working in terms of getting buffed.

I have seen other threads about the involvement of Decaying Hex, and what I was trying to do was combine it with Dispair. So i understand the spell decaying hex scales damage with intelligence as chaos damage. So why does it not increase in damage when your selecting nodes in the passive tree that "increase chaos damage"? The spell corrupting blood scales strength damage turning into physical damage over time. It gets buffed by flat "physical damage" nodes. Is this a bug that one is working and the other isn't?