Options of an ajax request are prepared through the ajaxSetup method, which uses jQuery.extend to create an independent instance. Unfortunately the given context property is also recursively cloned, although it gets discarded right afterwards.

Despite the fact that there might be a lot of unnecessary cloning going on, jQuery.extend does not know how to handle circular references. IE opens a stack overflow alert, Firefox informs about a too many recursions, Webkit just aborts the script path and continues like nothing happened.

#!div style="font-size: 80%"
Code highlighting:
  {{{#!js
    var obj = new Object();
    var obj2 = new Object();
    
    obj.myref = obj2;
    obj2.myref = obj;    

    var newObj = { };

    var s = jQuery.extend(true, {}, newObj, obj);
 

}}}

For now we suppressed deep cloning by adding a property "nodeType" to our context classes, which makes them look like DOM objects (at least for jQuery.isPlainObject).