[Dovecot] THREAD X-REFERENCES2 index bug?

[Nathan Kinkade]

Hi all,

$ sudo dovecot --version
1.2.beta3

I just started using Dovecot a few weeks ago, and my client is also using
the X-REFERENCES2 thread algorithm.  The client is misbehaving when trying
to list messages in my INBOX, but only when a threaded message exists.  I
have tracked it down to the thread index that Dovecot is returning, but the
problem is only extant when using the X-REFERENCES2 thread algorithm.  Here
is a snippet of transcript from imap client that comes with Dovecot:

$ export MAIL=maildir:~/Maildir:INBOX=~/Maildir/INBOX
$ /usr/lib/dovecot/imap
<snip>
1 SELECT "INBOX"
<snip>
2 THREAD X-REFERENCES2 UTF-8 ALL
* THREAD (0)(2)(1 3)(4)
2 OK Thread completed.

There are, in fact, only 4 messages in my INBOX, and the reference to (0)
seems spurious.  When I do the same test, but passing REFERENCES instead of
X-REFERENCES2 Dovecot returns an index which I believe to be correct:

<snip>
2 THREAD REFERENCES UTF-8 ALL
* THREAD (1 3)(2)(4)
2 OK Thread completed.
<snip>

Is this the normal and expected behavior of X-REFERENCES2 that the client
just needs to take into account, or is the reference to thread index (0) an
error?

Thanks!

Nathan