[Client] Game still starts when a player leaves during champion select

As the title said me and my friend encountered this bug in the (normal) draft pick champ select. When everybody in the lobby selected their champion and we got that 20 or so second to prepare, our mid-laner (first pick) left the room, but we still had time before the "prepare for battle" text appeared. Me and my duo-partner saw the same thing and we thought he dodged/dc-ed or something but the game started like nothing happened. In-game he was afk of course so we called open-mid becouse it was a pointless game. Not sure why did this happened but I only experienced it once, played before and after games without problem.