Drupal.ajax.prototype.commands.settings() empties Drupal.settings.ajaxPageState.css

I am working on an application heavily relying on the new Ajax framework in D7, and I am encountering an issue on subsequent ajax calls.

When there is no new CSS to be loaded in a Drupal ajax request, the returned settings.css in the response is an empty array. When this is merged with the current Drupal.settings.css - which is an object - in Drupal.ajax.prototype.commands.settings(), Drupal.settings.css becomes empty as well.

A small test I did with jQuery.extend():

      a = {
        css: { test: 1 }
      }
      
      b = {
        css: []
      }
      
      alert(JSON.stringify(a, null, 4));
      $.extend(true, a, b);
      alert(JSON.stringify(a, null, 4));

a before:

{
  "css": {
    "test": 1
  }
}

and a after:

{
  "css": []
}

Not good...

On any further ajax calls, no additional css will be loaded, because there is a check on $_POST['ajax_page_state']['css'], in ajax_render() in ajax.inc.

Not sure how to solve this best... Any ideas are welcome.