there is a bug on the client that if you write something in the chat then leave that chat and come back to it, whatever your wrote will stay. for instance:
if you write in champ select chat "hello" but before you click enter someone dodges, the next time you enter a queue that will be written down and you will just need to press enter. or if you write something in your group chat before entering a game, after ending the game when you go back to your group chat, it will still be written there. this is not a major bug but it is an inconvenience especially in blind pick, where you write "mid" and instead you wrote something like "whatmid" and then people might not understand what you meant.