[horde] pb with hook

[Service Informatique IF]

Hello,
I use Horde5 with the last revision get by pear

I try to activate the example in horde/config/hooks.php

in horde/config/prefs.d/10-webmail.php
i add :
$_prefs['from_addr']['hook'] = true;

and in horde/config/hooks.php

<code>
class Horde_Hooks
{
     // PREFERENCES INIT: See above for documentation.
     public function prefs_init($pref, $value, $username, $scope_ob)
     {
Horde::debug($pref);

// some dummy debug
$fileSim = fopen('/tmp/debug.txt','a+');
fwrite($fileSim,'on y est');
fclose($fileSim);
//
         switch ($pref) {
         case 'from_addr':

Horde::debug($pref);
$fileSim = fopen('/tmp/debug.txt','a+');
fwrite($fileSim,'on y est - 2 - ');
fclose($fileSim);

.....
</code>

But never the file for debug is written.

Can you help me ?

Thank you in advance.

PS; sorry for my english