[imp] Disable folder sharing in IMP

[lst_hoe02 at kwsoft.de]

Hello

we like to disable folder sharing in IMP and have therefore set the  
following in prefs.local.php


// *** ACL Preferences ***

$prefGroups['acl'] = array(
     'column' => _("General"),
     'label' => _("Share Folders"),
     'desc' => _("Share your mail folders with other users."),
     'members' => array('aclmanagement')
);

// ACL preference management screen
$_prefs['aclmanagement'] = array(
     'type' => 'special'
);

// folder sharing preferences
$_prefs['acl'] = array(
     // set 'locked' => true to disable folder sharing
     'locked' => true,
     'value' => ''
);

This does not work, folder sharing is still possible for users with no  
initial prefs. What have we done wrong?

Many Thanks

Andreas