Champion select bug

I can only assume this is a bug because i can't see how it would be in the game otherwise, but i played a game tonight that started as a 4v5. During champion select, after everyone had picked their champions, we received a message in the chat box saying that our top laner has left the room (he dc'd). Sure enough he doesn't load in with us. He was able to reconnect about 10-15 mins in and was trying, but by then we were too far behind and the enemy nasus was too far ahead from having a free lane for us to catch up. The whole champ select was revamped with gratuitous amounts of afk checks, but the game was still able to go through and start when one of our teammates had for all intents and purposes, left the game.