Drupal 7 ajax callback never ends
I've found a solution myself. Seems after the ajax callback the attach function is called again, so I surrounded by a jQuery .once() method:

(function($){

  Drupal.behaviors.myModule = {
    attach: function (context, settings) {

      $('#my_div', context).once('my_div', function () {
        var elem_settings = {};
        elem_settings.url = '/my_module_ajax_callback';
        elem_settings.event = 'load';
        elem_settings.keypress = false;
        elem_settings.prevent = false;

        var base = 'myModule';
        var ajax = new Drupal.ajax(base, this, elem_settings);
        Drupal.ajax[base] = ajax;

        $(this).trigger('load');
      });
    }
  }

})(jQuery);


This prevents calling the ajax once and over again.

https://drupal.org/node/756722#jquery-once

https://drupal.org/node/2192041