Emacs formatting strings - %s expansion

[Felipe Salvador]

Hi,
I use Mutt whit Emacs as editor, I'm trying to configure emacs in
order to make use of abook[1] via ExternalAbook[2].
I've folowed theese instructions[2], so I have:

(custom-set-variables '(external-abook-command "abook --mutt-query %s"))

When I run abook query from terminal I get this:

~$ abook --mutt-query emacs
 
help-gnu-emacs@gnu.org  lista-help-emacs

If I write "emacs" in emacs an then call
M-x external-abook-try-expand, I get this:

<lista-help-emacs>

Without email address. I suppose it could still work if I would keep aliases
file up to date, this is not the point.

I'm wondering why emacs expand ´$s´ in <lista-help-emacs>,
where <lista-help-emacs> is the fourth field in
"help-gnu-emacs@gnu.org  lista-help-emacs" string[3], when I would expect, at
least, the first one.

--
~$ emacs --version
GNU Emacs 25.1.1

~$ dpkg -l | grep emacs | awk '{print $2,$3}'
emacs25-bin-common 25.1+1-4+deb9u1
emacs25-common 25.1+1-4+deb9u1
emacs25-common-non-dfsg 25.1+1-1
emacs25-el 25.1+1-4+deb9u1
emacs25-nox 25.1+1-4+deb9u1
emacsen-common 2.0.8

[1] http://abook.sourceforge.net/
[2] https://www.emacswiki.org/emacs/ExternalAbook
[3] 
https://www.gnu.org/software/emacs/manual/html_node/elisp/Formatting-Strings.html

Regards

-- 
Felipe Salvador