dovecot - Apr 2010 - zero sized messages in Maildir, corrupt filenames ?

Hi,

I'm starting to see more and more duplicates in my cur directory. they 
seem to be a copy of an incoming mail (messages share the same date) but 
they appears in the client as a message without subject and without 
sender or body. Their filename starts with an underscore and the 4th 
letter is a %. The rest of the filename is random (but it also includes 
my hostname). Which program could create such a  filename ? If it's in 
the cur directory, it can only be dovecot, right ?

Example of 2 probably related messages in the cur folder:
1785 Apr 20 09:18 msg.zMeU:2,d
0 Apr 20 09:18 _J9C%jVVzLB.{myhostname}:2,

In addition, it seems that since we have started to use thunderbird 3, 
indexes are often corrupt, mailboxes needs reconstruction and so on. 
Could it be an incompatibility with my version of dovecot ? I've 
disabled my thunderbird filters that were moving the incoming mail 
automatically, no difference. I use no antivirus (linux imap client 
mainly). I can (probably) upgrade to dovecot-1.2.11-3_108 but I'd like 
to be sure that I won't create more problems before doing it.

The homedirs are NFS mounted.

dovecot 1.1.7-0_84
squirrelmail 1.4.19
postfix 2.6.5-1

Here is my dovecot -n
# 1.1.7: /etc/dovecot.conf
# OS: Linux 2.6.18-128.1.1.el5xen x86_64 Red Hat Enterprise Linux Server 
release 5.3 (Tikanga)
log_path: /var/log/dovecot.log
protocols: imap imaps
listen: *
login_dir: /var/run/dovecot/login
login_executable: /usr/libexec/dovecot/imap-login
mail_location: maildir:~/Maildir
mmap_disable: yes
mail_nfs_storage: yes
mail_nfs_index: yes
lock_method: dotlock
auth default:
  passdb:
    driver: pam
  userdb:
    driver: passwd
plugin:
  quota:

Thanks for your time,


-- 
Rodolphe Buret                  Ecole Polytechnique F?d?rale de Lausanne
System Administrator            EPFL STI-IEL-ESL
Tel: +41-21-693-0922            ELG 136 (b?timent ELG)
Fax: +41-21-693-0909            Station 11
Email: rodolphe.buret at epfl.ch   CH-1015 Lausanne Switzerland

On Tue, 2010-04-20 at 10:39 +0200, Rodolphe Buret wrote:
> Example of 2 probably related messages in the cur folder:
> 1785 Apr 20 09:18 msg.zMeU:2,d
This is an MH file.
http://wiki.dovecot.org/MailboxFormat/Maildir#Procmail_Problems
> 0 Apr 20 09:18 _J9C%jVVzLB.{myhostname}:2,
I don't know what this is. Not something created by Dovecot.

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