Symfony version(s) affected: 3.4/4.x

Description
I am in the progress of updating an app to Symfony 4 and the new flex directory structure.
Therefore I was trying to override the FOSUserBundle login template. This was not working
even with the file in the proper location according to the docs.

How to reproduce
I had templating enabled with twig as engine. The template was placed in /templates/bundles/FOSUserBundle/Security/login.html.twig and was not loaded.

While debugging I found out, that the functionality introduced in the TwigExtension to handle the proper loading as introduced in #24179 is not triggered.
It seems the TwigExtension is not loaded at all.

Possible Solution
Disabling the templating configuration of the framework bundle solved the issue for me.
Is this intended that this does not work with having the templating component enabled?