This occurred after the new patch installed.
When I am in chat, and I use an "!" exclamation point, everything prior to the punctuation gets erased, and only the exclamation point is sent in chat.
Getting same as well as two friends, all on the Mac client if that matters.
© 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.