This issue relates to http://symfony.com/doc/current/cookbook/templating/namespaced_paths.html

If you choose to render your templates using namespaced paths

{% extends "@AcmeDemo/layout.html.twig" %}

It means that if you create a new bundle that AcmeDemo is the parent of, it does not prepend the child bundle paths.

Eg, say I create AppDemoBundle which has a parent of AcmeDemoBundle it should check for the templates in @AppDemoBundle/layout.html.twig before it checks for @AcmeDemo/layout.html.twig