[Dovecot] Unable to use imapflags in sieve

[Guillaume Hilt]

   Hello,

I'm using dovecot 1.1.6 with libsieve 2.2.5 and I can't use the 
imapflags extension.
Here's the begginning of my .dovecot.sieve file :
require ["fileinto"];
#require "imapflags";
#require "reject";

#if header :contains "X-DSPAM-Probability: 0.9" {
#       addflag "$label3";
#}

# On déplace le spam dans le dossier Spam et on s'arrête là
if header :contains "X-DSPAM-Result" "Spam" {
       fileinto "Spam";
#       addflag "\\Seen";
       stop;
}

# Si le destinataire est l'user apache, on discarde le mail
if address :is "to" "[EMAIL PROTECTED]" {
       discard;
}

# Listes de diffusion
if header :contains "List-Id" "dovecot.dovecot.org" {
 fileinto "Listes.Dovecot";
 stop;
}

If i enable imapflags (require ["fileinto","imapflags"];) sieve won't 
work anymore (same with reject by the way).
Only enabling it without using it (with addflag) is enough to stop sieve 
from working. All my emails will be delivered in my inbox despite the 
rules I use. If I remove imapflags, everything is working fine.
And I don't see anything in my logs explaining the problem.