[Gameplay] Varus Q delayed release bug

So I played as Varus in Coop vs AI and i noticed a weird issue. As playing Varus I have noticed that his Q would always release when you let go of Q(i have quick cast). this time I held down Q like normal and let my Q charge up all the way. I then proceeded to let go of my Q and did not touch my keyboard and it took about 3 seconds for him to let go. I do not know how to set this bug up so that it would happen again because it seems random. It happened in 2 games.