How to reproduce
1) Type something into the chat window before game launches
2) Don't send it (don't hit enter)
3) Play game
4) Queue for 2nd game
When the chat window comes up it still has your unsent text in it.
© 2013 Riot Games, Inc. All rights reserved. Riot Games, League of Legends and PvP.net are trademarks, services marks, or registered trademarks of Riot Games, Inc.