I kinda think he means if he talks in lobby, once it reaches 11, 10... then it wipes everything you started to write. Basically, a slow writer, or a long sentence could ruin what was about to be typed to the lobby.
Ya the clearing the box is annoying. It be great if there was more time in the lobby or at least allow the server admins configure the time between rounds or disable countdown until more than 50% ready up. I think its way too short, you spend more time looking at your scores at the end of the game than chatting and organizing the next game....
Temporary work around; use the console. Code: Say my trash talk and blithering won't be cleared now! But yes, this annoys me immensely. I actually think with dedicated servers would might be better removing the lobby entirely. I'd also like to be able to chat during that 30 seconds of post-match and pre-lobby score screen.