[Dovecot] dovecot 1.1.3: File attachment truncated after moving the message into another folder

[Christoph.Jakobs at t-online.de]

Sometimes file attachments are truncated after moving the message from
one folder to another.

# 1.1.3: /usr/local/etc/dovecot.conf
ssl_disable: yes
disable_plaintext_auth: no
login_dir: /usr/local/var/run/dovecot/login
login_executable: /usr/local/libexec/dovecot/imap-login
first_valid_uid: 200
mail_privileged_group: mail
mail_location: mbox:~/mail:INBOX=/var/mail/%u
imap_client_workarounds: delay-newmail
auth default:
 passdb:
   driver: shadow
   args: blocking=yes
 userdb:
   driver: passwd