Deleting that chat session cookie will force the server to request the browser to create and store another cookie for that new session. Well we all know of impers that snag your favorite avatar URL and make them their own as they impersonate you. You reserve your favorite URLs and that can't happen.
However, some times when disconnected abruptly, or upon leaving and reentering too quickly (before the chat session has a chance to end), or just a chat session that gets hung up.
The easiest fix for this is merely deleting your cookies.