[Dovecot] Error: User doesn't have home dir set, disabling duplicate database

[fila at pruda.com]

Hello,

I have found this message in logs. But delivering is working.

Error: User peter at mydomain.cz doesn't have home dir set, disabling  
duplicate database

doveconf -n
# 2.0.8: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-lts i686  ext3
auth_mechanisms = plain login
disable_plaintext_auth = no
mail_location = maildir:/home/vmail/%u
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character  
vacation subaddress comparator-i;ascii-numeric relational regex imap4flags  
copy include variables body enotify environment mailbox date
passdb {
   args = /etc/dovecot/dovecot-sql.conf.ext
   driver = sql
}
plugin {
   home = /home/vmail/%u
   sieve = /home/vmail/%u/dovecot.sieve
   sieve_global_path = /home/vmail/dovecot-global.sieve
}
postmaster_address = postmaster at mydomain.cz
protocols = imap pop3
service auth {
   unix_listener auth-userdb {
     group = vmail
     mode = 0660
     user = vmail
   }
}
ssl_cert = </etc/ssl/dovecot/cert.pem
ssl_key = </etc/ssl/dovecot/key.pem
userdb {
   args = /etc/dovecot/dovecot-sql.conf.ext
   driver = sql
}
protocol lda {
   mail_plugins = sieve
}

I have googled little bit. According to this article  
http://wiki2.dovecot.org/VirtualUsers/Home
I think the problem is:
mail_location = maildir:/home/vmail/%u and plugin { home = /home/vmail/%u }
is the same directory.
Is it right?

Is the solution to set mail_location = maildir:/home/vmail/mail/%u ?

-- 
Best regards
Filip