Why is the invisible nunu bug in the game?

As you can see from the clip that i linked, Nunu was invisible until i was hit with his w. This has happened to me twice (once in two different games), and i believe that this is a game breaking bug. It seems to only happen early in the game. I wouldn't be surprised if it had to do with Nunu being unseen in the jg at the start. This bug should have been fixed a while ago.