mutt's buffy-list

[YONETANI Tomokazu]

Hello.
Since I have switched /home to a HAMMER PFS, mutt stopped reporting
mailboxes with new messages.  Digging mutt source code, I found something
relavant:

mutt_buffy_check:

    if (stat (tmp->path, &sb) != 0 || sb.st_size == 0 ||
        (!tmp->magic && (tmp->magic = mx_get_magic (tmp->path)) <= 0))
    {
      /* if the mailbox still doesn't exist, set the newly created flag to
       * be ready for when it does. */
      tmp->newly_created = 1;
      tmp->magic = 0;
      tmp->size = 0;
      continue;
    }

As HAMMER always reports st_size of directories to be 0, mutt thinks
that the mailbox is specified in $mailboxes but doesn't exist(yet).
My questions are, is checking st_size of a directory is usual on other
platforms/filesystems?  Does anyone know of other filesystems on which
a directory can have st_size of zero?

Cheers.