[Dovecot] fcntl Bad file descriptor

I've seen a couple of these in the log while testing the proxy too. Do you know what would cause this?

Aug 10 23:30:29 director5 dovecot: imap-login: fcntl(-1, F_GETFL) failed: Bad file descriptor Aug 10 23:30:29 director5 dovecot: imap-login: fd_set_nonblock(-1) failed: Bad file descriptor Aug 10 23:30:29 director5 dovecot: child 14016 (login) returned error 89