custom filter not triggering

Hello. In contacts module I added a field called active_c (checkbox). Then I tried to create a filter to display only the active contacts in list-view. The problem is, my filter never appears. What can cause this? Language file and filter is all according to documentation. The filter is defined in custom/Extension/modules/Contacts/Ext/client/base/filters/basic/filterContactsByActive.php and it looks like this:

  'id' => 'filterContactsByActive',
  'name' => 'LBL_ACTIVE_CONTACT',
  'filter_definition' => array(
      'active_c' => array(
        '$equals' => array(1)
  'editable' => true,
  'is_template' => true,

Do you have any ideea why it is ignored?