mime attachments get copied to new file name every time

Hello,

        I'm processing some mailing lists with procmail and
periodically running mhonarc on extracted mailboxes. Each time I
process a mail box, the attachments get copied to a new file, and the
old file remains. 

That is, the first time through, I had a file:

xls00000.xls

The next time, it creates xls00002.xls.

grep xls00002.xls *.html
msg00007.html:<!--X-Derived: xls00002.xls -->
msg00007.html:<P><A HREF="xls00002.xls"
> Project_Code_List-3-99.xls</A></P
A third time, and it create xls00004.xls
grep xls00004.xls *.html
msg00007.html:<!--X-Derived: xls00004.xls -->
msg00007.html:<P><A HREF="xls00004.xls"
> Project_Code_List-3-99.xls</A></P
So it looks like it always stays with same message number, but the
file is re-extracted each time.

Also, even though nothing has been added to the mailbox between runs
of MHonArc, most of the html files have a new timestamp. Are these
behaviors normal?

The only thing I saw in the FAQ what that messages could be added
twice if they did not have a Message-ID. This is not the case.

Thanks,

        Andy