Really strage bug that forced me to restart LoL

So I started an ARAM as the other day, and when the game started I pressed P to open the shop nothing happened. I hit escape, and nothing happened. I tried to move and it pinged instead. Then it suddenly swapped to windowed mode. Couldn't do anything other then ping. So I had to alt+F4 out, restart LoL, and then when I was back into the game everything was fine (Though I had to swap it back to full screen mode).