Symfony2 ajax and browser back button

I am following this article ( Symfony2: Ajax and Full Page Templates ) regarding using Ajax in my symfony2 web application.

As you can see in the article, I am expanding one template depending on the request (Ajax or not)

{% extends app.request.xmlHttpRequest ? 'DevmanagerCoreBundle::core-ajaxpage.html.twig' : 'DevmanagerCoreBundle::core-fullpage.html.twig' %}

      

        
        
        
      

    

To navigate the browser button, I am currently using the HTML5 History API.

Problem: when I click the back button (after the ajax call), why does symfony2 detect the request as xmlhttprequest?