removeClass from an extended Twig template seems not to work

API page: https://api.drupal.org/comment/reply/11564263

I have a custom Twig Paragraphs template which I use as base template. There I define the markup and add some classes to attributes and add the array later to the attributes object.

{#
/**
 * @file
 * Theme override for a field.
 *
 * To override output, copy the "field.html.twig" from the templates directory
 * to your theme's directory and customize it, just like customizing other
 * Drupal templates such as page.html.twig or node.html.twig.
 *
 * Instead of overriding the theming for all fields, you can also just override
 * theming for a subset of fields using
 * @link themeable Theme hook suggestions. @endlink For example,
 * here are some theme hook suggestions that can be used for a field_foo field
 * on an article node type:
 * - field--node--field-foo--article.html.twig
 * - field--node--field-foo.html.twig
 * - field--node--article.html.twig
 * - field--field-foo.html.twig
 * - field--text-with-summary.html.twig
 * - field.html.twig
 *
 * Available variables:
 * - attributes: HTML attributes for the containing element.
 * - label_hidden: Whether to show the field label or not.
 * - title_attributes: HTML attributes for the title.
 * - label: The label for the field.
 * - multiple: TRUE if a field can contain multiple items.
 * - items: List of all the field items. Each item contains:
 *   - attributes: List of HTML attributes for each item.
 *   - content: The field item's content.
 * - entity_type: The entity type to which the field belongs.
 * - field_name: The name of the field.
 * - field_type: The type of the field.
 * - label_display: The display settings for the label.
 *
 *
 * @see template_preprocess_field()
 */
#}


{%
  set classes = [
    entity_type|clean_class ~ '__ref',     // results in paragraph__ref
    'field',
    'field--name-' ~ field_name|clean_class,
    'field--type-' ~ field_type|clean_class
  ]
%}
{%
  set classes_item = []
%}


<ul{{ attributes.addClass(classes, 'field__items') }}>
  {% for item in items %}
    <li{{ item.attributes.addClass(classes_item, 'field__item') }}>
      {{ item.content }}
    </li>
  {% endfor %}
</ul>

Then I have some layout variants where I extend this base template and add a layout class.

{% extends "field--paragraph--para-ref.html.twig" %}

{% set attributes = attributes.addClass(entity_type|clean_class ~ '__ref--2col') %}

This works fine so far!

But there is one case where I need to remove a class in the extended template which is set in the base template.

{% extends "field--paragraph--para-ref.html.twig" %}

{% set attributes = attributes.removeClass('paragraph__ref').addClass(entity_type|clean_class ~ '__ref--width--full') %}

What I have experienced so far is that this does not work.

Am I doing something wrong or is this 'by design' not possible?