[Dovecot] dovecot trying to update my sieve directory

[Mathieu R.]

Hello,

i got an error in maillog, dovecot trying tu update my sieve directory 
:

2012-11-23T11:01:33.943047+00:00 localhost dovecot: 
imap(mathieu at 400iso.net): Error: 
stat(/srv/vmail/400iso.net/mathieu at 400iso.net/.dovecot.sieve/tmp) 
failed: Not a directory

this cause no problem but i probably misconfigured something...
here is my dovecot.conf :


protocols = imap pop3 sieve

mail_home = /srv/vmail/%d/%u
mail_location = maildir:~
mail_plugins = $mail_plugins quota

ssl_cert = </etc/ssl/private/server.crt
ssl_key = </etc/ssl/private/server.key

service auth {
   unix_listener auth-client {
     group = postfix
     mode = 0660
     user = postfix
   }
   user = root
}

passdb {
   args = /etc/dovecot/dovecot-sql.conf
   driver = sql
}

userdb {
   args = /etc/dovecot/dovecot-sql.conf
   driver = sql
}

protocol lda {
       mail_plugins = $mail_plugins sieve
       postmaster_address = postmaster at 400iso.net
       hostname = 400iso.net
}

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 ihave

plugin {
   sieve = ~/.dovecot.sieve
   sieve_dir = ~/sieve
#  sieve_global_dir = /srv/vmail/sieve/
   quota = fs:vm quota
   quota_rule = *:storage=5G
}


protocol imap {
         mail_plugins = $mail_plugins imap_quota
}

-- 
Mathieu Rousseau
http://400iso.net/