i had this warning while updating to beta2 and switch to dovecot:
QuoteServers::po::dovecot::installer::migrateMailboxes: Use of uninitialized value $_ in scalar chomp at /var/www/imscp/engine/PerlVendor/courier-dovecot-migrate.pl line 197, <$f> line 1.
/var/mail/virtual/my.tld/admin/courierpop3dsizelist: Broken header: /2 1 1337883711
but system seems to work correctly