Every time a message is composed and sent to a IMAP server the composition tab on the task bar does not go away. It cannot be selected to close.
Additional noted: It seems to happen for all types of email compositions. Whether it is an IMAP or POP server. Even happens for forwards and replies. The title shown for the tab in the task bar just changes names to the last subject line sent.
*** This bug has been marked as a duplicate of 130572 ***