Varus Q cooldown bug

I was playing Varus, and as you know if you hold down his Q long enough you get a CD, and mana refund. Well if you release the arrow at last second you get both the CD reduc and still shoot the arrow. I have tested this in several different matches and I have been able to recreate it everytime. Not sure if this is a bug or if it was intentional; just though it should be brought to peoples attention.

tl;dr: Release varus Q last second shoot arrow, still get cd reset.