Error when adding first RootPage with multiple locales activated

[ghost]

Whenever I have no pages (see below image)

and try to add one, with multiple locales set in the locale setting

I get the following error:

Internal Server Error: /admin/pages/add/app_cms/pageroot/1/
Traceback (most recent call last):
  File "C:\Work\virtual_env\lib\site-packages\django\core\handlers\exception.py", line 47, in inner
    response = get_response(request)
  File "C:\Work\virtual_env\lib\site-packages\django\core\handlers\base.py", line 179, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Work\virtual_env\lib\site-packages\django\views\decorators\cache.py", line 44, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File "C:\Work\virtual_env\lib\site-packages\wagtail\admin\urls\__init__.py", line 127, in wrapper
    return view_func(request, *args, **kwargs)
  File "C:\Work\virtual_env\lib\site-packages\wagtail\admin\auth.py", line 193, in decorated_view
    return view_func(request, *args, **kwargs)
  File "C:\Work\virtual_env\lib\site-packages\django\views\generic\base.py", line 70, in view
    return self.dispatch(request, *args, **kwargs)
  File "C:\Work\virtual_env\lib\site-packages\wagtail\admin\views\pages\create.py", line 96, in dispatch
    return super().dispatch(request)
  File "C:\Work\virtual_env\lib\site-packages\django\views\generic\base.py", line 98, in dispatch
    return handler(request, *args, **kwargs)
  File "C:\Work\virtual_env\lib\site-packages\wagtail\admin\views\pages\create.py", line 104, in post
    return self.form_valid(self.form)
  File "C:\Work\virtual_env\lib\site-packages\wagtail\admin\views\pages\create.py", line 110, in form_valid
    return self.publish_action()
  File "C:\Work\virtual_env\lib\site-packages\wagtail\admin\views\pages\create.py", line 151, in publish_action
    self.parent_page.add_child(instance=self.page)
  File "C:\Work\virtual_env\lib\site-packages\treebeard\mp_tree.py", line 1022, in add_child
    return MP_AddChildHandler(self, **kwargs).process()
  File "C:\Work\virtual_env\lib\site-packages\treebeard\mp_tree.py", line 389, in process
    newobj.save()
  File "C:\Users\AppData\Local\Programs\Python\Python37\lib\contextlib.py", line 74, in inner
    return func(*args, **kwds)
  File "C:\Work\virtual_env\lib\site-packages\wagtail\core\models.py", line 1005, in save
    result = super().save(**kwargs)
  File "C:\Work\virtual_env\lib\site-packages\modelcluster\models.py", line 196, in save
    super(ClusterableModel, self).save(update_fields=real_update_fields, **kwargs)
  File "C:\Work\virtual_env\lib\site-packages\django\db\models\base.py", line 754, in save
    force_update=force_update, update_fields=update_fields)
  File "C:\Work\virtual_env\lib\site-packages\django\db\models\base.py", line 803, in save_base
    update_fields=update_fields, raw=raw, using=using,
  File "C:\Work\virtual_env\lib\site-packages\django\dispatch\dispatcher.py", line 179, in send
    for receiver in self._live_receivers(sender)
  File "C:\Work\virtual_env\lib\site-packages\django\dispatch\dispatcher.py", line 179, in <listcomp>
    for receiver in self._live_receivers(sender)
  File "C:\Work\virtual_env\lib\site-packages\wagtail_localize\synctree.py", line 213, in on_page_saved
    locale, copy_parents=True, alias=True
  File "C:\Users\AppData\Local\Programs\Python\Python37\lib\contextlib.py", line 74, in inner
    return func(*args, **kwds)
  File "C:\Work\virtual_env\lib\site-packages\wagtail\core\models.py", line 2325, in copy_for_translation
    reset_translation_key=False,
  File "C:\Work\virtual_env\lib\site-packages\wagtail\core\models.py", line 2210, in create_alias
    alias = parent.add_child(instance=alias)
  File "C:\Work\virtual_env\lib\site-packages\treebeard\mp_tree.py", line 1022, in add_child
    return MP_AddChildHandler(self, **kwargs).process()
  File "C:\Work\virtual_env\lib\site-packages\treebeard\mp_tree.py", line 389, in process
    newobj.save()
  File "C:\Users\AppData\Local\Programs\Python\Python37\lib\contextlib.py", line 74, in inner
    return func(*args, **kwds)
  File "C:\Work\virtual_env\lib\site-packages\wagtail\core\models.py", line 982, in save
    self.full_clean()
  File "C:\Work\virtual_env\lib\site-packages\wagtail\core\models.py", line 948, in full_clean
    super().full_clean(*args, **kwargs)
  File "C:\Work\virtual_env\lib\site-packages\django\db\models\base.py", line 1233, in full_clean
    raise ValidationError(errors)
django.core.exceptions.ValidationError: {'path': ['Page with this Path already exists.']}

With the following Page:

class PageRoot(Page):
    subpage_types = [
        'app_cms.PageCustom',
        'app_cms.PageBlogListing',
    ]

    class Meta:
        verbose_name = _('root page')
        verbose_name_plural = _('root pages')

    def __str__(self):
        return self.title