Perhaps a rewrite to clarify? What happens if the client arbitrarily closes the connection? Does that result in a closed state? I think it would be clear if rearranged as follows.

This state is entered upon a "QUIT" command, a server or client arbitrarily closing the connection, or a session timeout.

However, I must check to determine whether the client closing the socket will automatically cause the server's socket to close.

Client closing without warning is an error which should not be addressed in the spec. - dave

Issue done.