Diana Passive Bug on Inhibitor

So, I was playing in a One for All match earlier today, and our team picked Diana. We ended up getting into the opposing team's base and I started to attack the inhibitor. I noticed that on every 3rd hit my passive would go off on the inhibitor and would not deal the extra magic damage. I know that Diana's passive is supposed to work on enemy structures, so I tried to figure out what was wrong. I moved as close as I could to the inhibitor before attacking again, and it turns out the bonus magic damage started to apply every 3rd hit like its supposed to. I concluded that if you are attacking an inhibitor as Diana, you will not proc her passive damage on it if you are attacking at max auto attack range. I tested this on multiple inhibitors with the same result. Very easy to replicate.