Garen can't Q the nexus. (ARAM)

While closing a game of immortal man smacks things, I noticed that I had stopped hitting the enemy nexus. A couple seconds later, it happened again.

The third time, I paid a bit more attention than I was to enemies, and noticed it was when I hit Q for the reset (MOAR DPS!!!).

So in short, Garen cannot hit the purple nexus on Howling Abyss while he has Decisive Strike ready.