Profane Bloom bug?

I got my profane bloom forbidden flesh/flame and was using with inpulsa's and it was fine. I wanted to swap out my inpulsa's and realized profane bloom was not really working. It seems like if you one-shot the mob it doesn't go off, you can see the mobs body get cursed like .2 seconds after. I have an elemental weakness on hit ring so all damage should curse.

Is this intentional?