Of all the settings I have seen on the Admin page, timeout settings was not one of them. It must have been quite a large rant. I don't want others getting paranoid about their messages.
I would suggest any large letters be type in "Notepad". Then, just copy and paste it into the message window. Not only can it timeout as you have found, but you could accidentally "Back" to the webpage before and bleaping yourself, too. You dig, Doug?