[GAMEPLAY] After using E, Quinn's auto-attack deals no damage

I recently played a match with Quinn. Ingame I used "Vault" on the enemy (Teemo) and landed properly. Then I autoattacked Teemo to proc "Harrier" but when the projectiles hit, no damage was dealt and "Harrier" stayed active. First I thought I had missclicked but after three times this happened I got confused. After about 1 second after landing and shooting the aa that deals no damage, the next aa hits as it is supposed to and procs "Harrier". I don't know if this is an meant mechanic but for me it looked pretty much like a bug. In a replay of this gameplay I saw this "bug" as well, so it shouldn't be just a graphic bug.