[vox-tech] procmail question: filtering message mangles headers

[hajhouse@houseag.MAPScom (Henry House)]

I have the following procmail recipes to create a makeshift mailing list:

:0:
* ^To:.*m10-update
* !^X-Loop: m10@houseag.com
* ^Received: from wotan.hajhouse.org   # accept messages from my host only
{
      :0c
      updates.mbox

      :0fh
      | sed -e 's/^Subject: /Subject: \[M-10\] /'

      :0
      ! `$HOME/_sendmails`
}

The first recipe in the bracketed block archives to a mailbox and the third
forwards the message to the list of addresses produced by the script
_sendmails.

The second recipe is supposed to tag the subject header of incoming messages to
make them easy for their recipients to identify, just a many mailing lists do.
It does not work! Instead the messages are mangled---the subject is completely
blank and the To: and From: headers are re-written. This does not happen when I
comment-out the second recipe.

Offhand, I see no reason for this difference in behavior either in the recipes
or in the logfile. Clearly I am missing some subtlety. Can anyone enlighten me?

-- 
Henry House
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