[Dovecot] Emails Disappearing -- Mystery

[Mario Antonio]

I got a case that I haven't  been able to resolve. I  hope somebody can 
give me some hints.

One of our users is reporting emails disappearing in front of his eyes,  
(Right ...  emails filters at the client side ....)

Server does not have global sieve filter enabled (no file present), even 
though this configuration is present:
   sieve_global_path=/vmail/globalsieverc

User does not have any sieve scripts enabled at the server side.

Ok,

1)
The user shuts down his apple mail software, his Iphone, and the Web 
interface:

2010-03-11 15:52:57 IMAP(my_user at mydomain.com): Info: Connection closed 
bytes=2188/6499
2010-03-11 15:52:57 IMAP(my_user at mydomain.com): Info: Connection closed 
bytes=3887/7336
2010-03-11 15:52:57 IMAP(my_user at mydomain.com): Info: Connection closed 
bytes=5873/68309
2010-03-11 15:52:57 IMAP(my_user at mydomain.com): Info: Disconnected in 
IDLE bytes=4514/547136

2)
He generates the troublesome emails from a notification system in 
Craiglist ....
We can see the email hitting the inbox (we also see in Postfix this 
email going to Dovecot)
2010-03-11 15:54:48 deliver(my_user at mydomain.com): Info: 
From=noreply at craigslist.org : 
msgid=<20100311205447.0C0FE118B04 at web8p.int.craigslist.org> : saved mail 
to INBOX

3)
Email is deleted !!!
2010-03-11 15:54:49 IMAP(my_user at mydomain.com): Info: delete: uid=10719, 
flags=(\Deleted \Recent $Junk),
msgid=<20100311205447.0C0FE118B04 at web8p.int.craigslist.org>, 
from=craigslist.org <noreply at craigslist.org>, subject=POST/EDIT/DELETE : 
(accounting/financejobs) Test Post
2010-03-11 15:54:49 IMAP(my_user at mydomain.com): Info: expunge: 
uid=10719, flags=(\Deleted \Recent $Junk),
msgid=<20100311205447.0C0FE118B04 at web8p.int.craigslist.org>, 
from=craigslist.org <noreply at craigslist.org>, subject=POST/EDIT/DELETE : 
(accounting/finance jobs) Test Post , size=2776

Who is deleting this email ?
I can see the flag $Junk ... perhaps some filter somewhere is seeing 
that flag and proceeding to delete it.
If I understand sieve filters at the server side, they will act in the 
deliver process. So once the email is saved into INBOX,  sieve filters 
will not count. Am I right?

Any Hints?

# 1.2.9: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.26-2-686-bigmem i686 Debian 5.0.4 xfs


Regards,

Mario Antonio