JQuery related "invalid foreach in menu.inc on line 258" problem... and an AJAX combo binding example

I'm experience a big problem in latest versions of D6 (I've tested it in D6.3 and D6.4). I have searched and it's not new... it's related to the new menu system?? Look at http://drupal.org/node/272821

The thing is when you write a form that involves some JS, a lot of warnings of the type "warning: Invalid argument supplied for foreach() in F:\xampplite\htdocs\d2\includes\menu.inc on line 258." become to appear...

For you to test it, I've written a "demo" of the behaviour I want to write, but by the way it's affecting to other modules behaviour like ActiveSelect (there's a port to D6 with the same issue)

The example is simply a form with 2 selects, parent and children that when you change the value in parent, the children does an ajax request to modify its values:

test.info

; $Id$
name = "Test"
description = "Test"
core = 6.x
php = 5.1

test.module

function test_menu() {
  $items = array();
  $items["test/form"] = array(
    'title'    => t('Test form'),
    'type'     => MENU_NORMAL_ITEM,
    'page callback' => 'drupal_get_form',
    'page arguments' => array('buildTestForm'),
    'access arguments'   => TRUE,   
  );
  $items["test/json/%"] = array(
    'type'     => MENU_CALLBACK,
    'page callback' => 'getJSON',
    'page arguments' => array(2),
    'access arguments'   => TRUE,   
  );
  return $items;
}

function getJSON($parentKey) {
  if ($parentKey === "keySoccer") {
    $terms = array(
      "Messi",
      "Ronaldinho",
    );
  } else if ($parentKey === "keyBasketball") {
    $terms = array(
      "Jordan",
      "M. Johnson",
    );
  }
  print drupal_to_js($terms);
  exit();
}

function buildTestForm() {
  drupal_add_js(drupal_get_path('module', 'test') .'/test.js');
  
  $form['parent'] = array(
    '#type' => 'select',
    '#title' => t('Parent'),
    '#options' => array(
      "keySoccer" => "Soccer",
      "keyBasketball" => "Basketball",
    ),
  );
  $form['child'] = array(
    '#type' => 'select',
    '#title' => t('Child'),
    '#options' => array(),
    '#DANGEROUS_SKIP_CHECK'=>true,
  );

  return $form;
}

test.js

if (Drupal.jsEnabled) {

    function searchSubTerm(parentSelect, targetSelect) {
      $.getJSON(  "/XXX/test/json/"+parentSelect.val(), {id: $(this).val(), ajax: 'true'}, function(j) { //Check the url to your menu!!!
        var options = '';
        for (var i = 0; i < j.length; i++) {
          options += '<option>' + j[i] + '</option>';
        }
        targetSelect.html(options);
      })
    }
    
    $(document).ready( function() {

        $(function() {

          $("#edit-parent").change(function() { 
            searchSubTerm($("#edit-parent"),$("#edit-child"));
          });        

        });
        
    });

}

This is an example of the behaviour I want, the "real" thing is to get to work a navigation across the terms of a certain vocabulary for a custom search of a custom node type... for example in a node type CAR, a block to search them by the fuel type, or make/model/version, etc

Do anyone know what happens with menu system? Is it a bug? What can I do? I've spent a lot of hours looking for a solution...

Thank you very much
Juan Arias
Spain