Ghost emails

[Giuseppe Ravasio]

Hi,
I'm running a Postfix+Cyrus+Ldap Auth mail (IMAP) server on a Suse 9.1 with 
about 200 users.
The software versions are:
cyrus-imapd-2.2.3-83.22
postfix-2.1.1-1.20

It's working fine since 2005, but now i'm facing a strange problem on a user 
mailbox. 
An email is received by the MTA, then postfix delivers this email to CyrusImap 
with /usr/lib/cyrus/bin/deliver.
From the /var/log/messages i see:

May 31 20:37:37 server lmtpunix[31094]: accepted connection
May 31 20:37:37 server lmtpunix[31094]: lmtp connection preauth'd as postman
May 31 20:37:37 server lmtpunix[31094]: duplicate_check: 
<86D6BCB7F53B8D46980FE134992AA0020395DB3A at AMAILSERVER.it> user.beppe       0

May 31 20:37:37 server lmtpunix[31094]: mystore: starting txn 2147483677
May 31 20:37:37 server lmtpunix[31094]: mystore: committing txn 2147483677
May 31 20:37:37 server lmtpunix[31094]: duplicate_mark: 
<86D6BCB7F53B8D46980FE134992AA0020395DB3A at AMAILSERVER.it> user.beppe       
1180636657 43699

May 31 20:37:37 server lmtpunix[31094]: mystore: starting txn 2147483678
May 31 20:37:37 server lmtpunix[31094]: mystore: committing txn 2147483678
May 31 20:37:37 server lmtpunix[31094]: duplicate_mark: 
<86D6BCB7F53B8D46980FE134992AA0020395DB3A at AMAILSERVER,it> .beppe+ at .sieve. 
1180636657 0

So it seems that the message was correctly delivered, and in fact in the user 
FS folder there is a file containing the email!
But this email doesn't appear via IMAP, and the only way to make it visible 
was:

reconstruct -f user/beppe

It isn't the first time that i've this strange behaviour, and since today i 
saw this issue only on a single user folder.
Any ideas?

Thanks
G.Ravasio