Test CheckBox on NestedTree fails

I built my tree application based on the NestedTree example from http://ift.tt/1Mey5ml, but i'm struggling at testing this component using WicketTester.

With WicketTester i trigger the AJAX event on the CheckBox:

tester.executeAjaxEvent("path:to:checkbox", "onclick");

The AjaxCheckBox onUpdate event is fired as well, but it's model doesn't change.

A simple page with an AjaxCheckBox and PropertyModel works fine, the model changes as expected:

add(new AjaxCheckBox("check", new PropertyModel<>(this, "checked")));

Is it impossible to test this component with WicketTester?