Rengar Q Bug

Hello! So me and my friend where playing around playing stealth champions. I chose Shaco and he chose Rengar . So we were pushing towers when my friend found a bug. If you hit Q then attack towers you attack the tower 2 times in a row very quickly with the Q buff, then a 3rd time a bit later still with the attack buff.

1. Push wave to tower
2. Hit Q
3. Attack the tower

The bug works everytime i try it. I tried several times. Here is a link to a youtube video with the bug. [https://www.youtube.com/watch?v=zg2emp-BkaU]

I am sorry if this is not an actual bug but i don't see anything regarding it in the description of the ability.