Ludens Echo needs some tweaks and clarification

So on the wiki, it states: At 100 charges, the next instance of ability damage you deal will expend all charges to deal 100 (+ 15% AP) bonus magic damage In game it states At 100 charges, the next spell hit expends all charges to deal 100 (+ 15% AP) bonus magic damage

As far as i've found through testing, this is what I have found. Ludens will proc off of physical damage spells (Example: Aatrox Q) But not on-hit spells like Ezreal Q It will proc off magic damage items, (IE Thornmail/Sunfire)

So how much of this is intended and how much of this is bugged?