Locked in lobby, I can't leave/stop the "Find Match"

I just finished a game of ARAM and Q'd for another, everything was working fine. I noticed while watching a Youtube video in the background that it was taking quite a while to find a match so I checked the client and it had been searching for over 10 minutes. I decided to stop the search and then rejoin, but to my surprise, I couldn't stop the "Find Match"

I pressed the 'X' in both the lobby screen and the top right corner-- nothing worked. I could flip between tabs and even enter the store, but I couldn't get the client to stop looking for a match.

God, that's annoying.