Deathfire Touch (Possible bug)

I've noticed that quite a few moves don't proc Deathfire Touch; a couple of examples being Miss Fortune's Q and Ezeral's Q. I am not sure if this is necessarily a bug (due to both abilities applying on-hit affects), but I kind of think it is because the tooltip just lists damaging abilities and spells, so I don't see why that wouldn't apply to abilities that are targeted or shot at enemy champions.