Setting fluid container creates duplicate container inside navbar

Create a site with navbar location set to normal/default and fluid containers, your container class gets repeated twice eg:

<header class="navbar navbar-inverse container-fluid" id="navbar" role="banner">
<div class="container-fluid">
...

Mistake is templates/system/page.html.twig:71

    <header{{ navbar_attributes.addClass(navbar_classes) }} id="navbar" role="banner">
      {% if not navbar_attributes.hasClass('container') %}
        <div class="{{ container }}">
      {% endif %} 

You are only checking to see if the container class has been applied previously, whereas it should test container and container-fluid.