[Dovecot] Dovecot out of memory errors on Debian sid

[Ric]

hi

I have dovecot (1.0.alpha4-1) installed on a Debian sid amd64 machine
(dovecot-imapd and dovecot-common).  I am using this so that I can use both
Mutt and something like Thunderbird to access my local Maildir folders.
Sometimes it works fine.  Sometimes when I try to access my mailboxes locally
using Mutt, it hangs for a very long time (the bottom of the screen says
"Selecting in..." (.in is the mailbox), and eventually gives me a blank
mailbox with "(no mailbox)" at the bottom of the screen.  In
/var/log/mail.err I find lines like the following:
    Dec  3 06:39:02 localhost dovecot: child 4600 (imap) returned error 83 
        (Out of memory)
    Dec  3 06:44:03 localhost dovecot: imap(ric): pool_system_malloc(): Out 
        of memory
For example, it was working fine earlier this morning, but now I am unable to
access the mailboxes and I'm getting the error messages in /var/log/mail.err.

I have the same problem with Thunderbird; it hangs and cannot access the
mailboxes.  

At my office I have dovecot (0.99.14-1) installed on a Debian sarge machine
and it works fine.

I would appreciate any suggestions as to what to try or what to look for.
My dovecot.conf file is very simple:

## Dovecot 1.0 configuration file
protocols = imap 
listen = localhost
ssl_disable = yes
log_timestamp = "%Y-%m-%d %H:%M:%S "
mail_extra_groups = mail
protocol imap {
}
protocol pop3 {
}
auth default {
  mechanisms = plain
  passdb pam {
  }
  userdb passwd {
  }
  userdb prefetch {
  }
  user = root
}

Thanks,
Ric