Summoner's Rift ending screen frozen (MAC client)

It happened to me after finishing a classic game (never happened with the poro game). The screen was frozen, but my mouse could move, my music still worked (and I could still shuffle), and the Rift sound still played. But it was frozen on the screen so that I couldn't minimize it, switch screens, or try to force quit it. I had to restart my computer to get out of it.

Is it just a problem with my Macbook (so I can take it to the shop), or is it the client?