@Meddler: Zac's Q

Since no one wants to comment on my question in the bugs forum I figured I would actually address this to you personally. So recently I've been experimenting with Zac in the top lane. He definitely is a lot of fun but I encountered a very peculiar bug while testing out an item.

While fighting most enemies I could target a minion with Q first then target the enemy 2nd and crash them together. But this is where I found some discrepancy with how his 2nd Q works. When I bought the item passive would not proc on the 2nd on hit Q which leads me to believe that the 2nd portion of his Q is still, in fact, a skill. So an auto attack afterwards was necessary to proc .

But!! When facing , the 2nd part of Zac's Q was actually blocked by passive. Which that would suggest that his 2nd Q is not a skill but an auto attack.

So....here's the question: Is Zac's 2nd Q a skill that should not be blocked by passive? -OR- is it an auto attack that should also proc similar to Q?