Use of __salt__['pillar.filter_by'] in pillar stack

[achinayoungwaubonsee]

We have salt 2019.2.0:

# salt --version
salt 2019.2.0 (Fluorine)

/srv/pillar/stack/httpd.yml has:

# cat /srv/pillar/stack/httpd.yml
{% load_yaml as httpd_definitions %}
web_servers:
  enable: true

default:
  enable: false
{% endload %}

{% set httpdnew = __salt__['pillar.filter_by'](httpd_definitions,
                                               pillar='roles') %}
httpdold:
{% if (pillar.get('roles') and
       ('web_servers' in pillar.get('roles'))) %}
  enable: true
{% endif %}

httpdnew: {{ httpdnew | json() }}

# salt <id> pillar.items
    httpdnew:
        ----------
        enable:
            False
    httpdold:
        ----------
        enable:
            True
    roles:
        - web_servers
        - dev_web_servers

Why isn't __salt__['pillar.filter_by'] working? I would expect httpdnew.enable=True, the same as httpdold.enable.