shutdown patch

[Night OWL]

I have just upgraded from version 2.1.11 to 2.1.13 of cyrus-imapd, and
now I have lines like this in my maillog:

  May 26 21:54:36 ns imapd[20318]: Could not shut down filedescriptor 0: Transport endpoint is not connected
  
for file descriptor 0, 1, 2 when an imap session is started, but users
can still access their mailboxes using imap.

I do no undertand what this lines stand for. Probably, this is
because of "The shutdown patch" mentioned in doc/changes.html?
Could you please explain me. Have I done something wrong?

Maxim