Odd Cc: behaviour

[Anthony Edwards <anthony@xxxxxxxxxxxxxxxxxxxxx>]

I like, since it makes archiving threads quick and easy, to cc: myself
automatically on all emails that I send.  I am able to do this using
Mutt on all machines on which I have accounts except one.

The one I can't, runs Mutt 1.5.4i on Debian (I believe unstable).  The
relevant .muttrc:

  ---- begin .muttrc ----
set spoolfile="~/Mail/inbox"
set mbox_type=Maildir
set folder="~/Mail"
set record="=sent-mail"

set copy=yes

folder-hook  .   "my_hdr From: Anthony Edwards <anthony@xxxxxxxx>"
folder-hook  .   "my_hdr Cc: Anthony Edwards <anthony@xxxxxxxx>"

set editor="vim -c 'set tw=72'"

set mime_fwd=ask-yes

set pager_index_lines=0

unignore from date cc
set edit_hdrs
set sort=threads

unset beep
unset move
unset autoedit
set fast_reply
unset write_bcc

set signature=~/.signature

source ~/.mail_aliases
set alias_file=~/.mail_aliases

color hdrdefault brightcyan black
color status    brightyellow   blue
color indicator magenta  black
color quoted    cyan      black
color quoted1   yellow    black
color quoted2   red       black
color quoted3   green     black
color quoted4   cyan      black
color quoted5   yellow    black
color quoted6   red       black
color quoted7   green     black
color tilde     green     black
color signature brightred     black
  ---- end .muttrc ----

When sending new mail, the above my_hdr Cc: command works however, when
replying to mail, it does not.

I have just spent the last two hours Googling and reading the manual,
plus looking at the machine's /etc/Muttrc file, in an attempt to
work out what is causing this but have been so far unable to come up
with anything.

Does anyone have any ideas?

-- 
Anthony Edwards
anthony@xxxxxxxxxxxxxxxxxxxxx