[Dovecot] All mails unread after short while

[francwalter at gmx.net]

Hello,

I have on Ubuntu 8.04 Postfix 2.5.1 and Dovecot 1.0.10.
The mails are saved in maildir format.

In one account on my server all mails are unread all the time. If i set them as read in my client (IMAP with Mac Mail 4.4 or IMAP with Squirrelmail, it doesn’t matter) they seem to be checked as read for some minutes or less, but very soon they are unread again, so i guess, only my client thinks that they are read, but after the next check, the client reads again that they are unread.

Now i don’t know where to look or change the “Has been read”-Flag in the maildir-directory.
Is it in some file or where is it, the flag?

It is only one account, the other accounts on the same domain and on other domains are working quite well. 
Maybe it is only after a Squirrelmail update last week, but I am not sure.

Thank you, 

Kind Regards,

frank walter