This is a very minor UI bug, but it is easy to reproduce.
Windows 7 x64, Firefox 29.
- Open the profile of another player during a game.
- Click the envelope icon to begin a new conversation.
- At any point from here composing the subject or the message body, press the “Clear” button.
The Send button will be disabled until you reload the page in the browser, or visit an ongoing conversation through the message menu, at which case the Send button will begin working again for existing and new conversations.
Perhaps a clue: this does not happen when composing a new message via the “New Message” button on the Inbox menu.
Maybe there is less utility in even having a Clear button for new conversations initiated from the profile page, since there isn’t a selection process for adding names of other players.