Gameplay Diana bug?

I was using Diana in the mid lane yesterday and I was trying a new item set. I had Nath tooth in my items. It works very well with her passive. However when I was taking down a turret and inhib. I noticed it went off either every swing or every third and sometimes not at all. I didn't even know her passive or nashor passive could even activate on turrets and inhibs. Was my first time using her and no one in that match could tell me if it was a bug or not so I am submitting a report.