How do form #states interact with dialog action buttons, if at all? A dialog can be fired by a link formatted as such:

&lt;a class="use-ajax" 
    data-dialog-options="{&amp;quot;width&amp;quot;:400}" 
    data-dialog-type="modal" 
    href="/some/path"&gt;
    Some path displayed in modal dialog.
&lt;/a&gt;


If the contents of /some/path are a form, then drupal takes its action buttons and drops them into a "footer" &lt;div class="ui-dialog-buttonset"&gt;&lt;/div&gt; in the dialog. This seems to take into account the initial state of the buttons -- so if submit has the disabled attribute by default then the corresponding UI button gets the .is-disabled class applied. The "real" form action buttons are rendered but set to display: none. 

However, I've got #states set up on my submit button with 

$form['actions']['submit']['#states'] = [
  'disabled' =&gt; [
    ':input[name="field_fivestar_rating[0][rating]"]' =&gt; [
      [
        ['value' =&gt; '-'],
        ['OR'],
        ['value' =&gt; '0'],
      ],
    ],
  ],
];


The "real" form submit button is updated correctly according to its #states attribute, but the same cannot be said for the corresponding dialog button. It seems to be static based on the initial state of the submit button.

Is this expected behavior? If so, is this something that deserves an issue in the queue? Seems like an oversight and usability concern.
This doesn't answer the question itself, but since I struggled for a while to get this all syncd up I figured I should drop the work into something that people might hit from google. To get the attributes all syncd up you can use the following js file:

(function ($, Drupal, drupalSettings) {
  var handler = Drupal.behaviors.commentsRatingFlexible = {
    attach: function (context, settings) {
      // If our form is loaded in a modal, then the context is
      // the form itself. Therefore we cannot look for the form
      // inside of context. As such, we need to check for forms
      // that exist in both situations an handle accordingly.
      var formInstances = [];

      // This would be the class for your particular form
      $('.comment-rating-flexible-form', context).each(function () {
        formInstances.push($(this));
      })

      if ($(context).hasClass('comment-rating-flexible-form')) {
        formInstances.push($(context));
      }

      // Lookup any rating-flexible-forms and disable the submit
      // button by default, since it shouldn't allow an empty val
      // for the fivestar field (if it's present)
      for (var k in formInstances) {
        var $form = formInstances[k];
        var $submit = $('.form-submit', $form);
        var $fivestarSelect = $('[name="field_fivestar_rating[0][rating]"]', $form);

        if (!$fivestarSelect.length) {
          return
        }

        handler.dialogSubmitButtonHandler($form); //must be called first
        handler.observeAttributes($submit);

        if ($fivestarSelect.val() == '-' || $fivestarSelect.val() == '0') {
          // #states don't apply on form load, only on change, 
          // so we need to disable the form button here and 
          // sync that onto the dialog's button
          $submit.attr('disabled', "");
        }
      }
    },
    /**
     * Syncs attributes from real form-submit onto dialog submit btn.
     *
     * @param $form
     *   The form contained in the dialog
     */
    dialogSubmitButtonHandler: function ($form) {
      var $drupalModal = $form.parent();

      // If the form is loaded outside the context of a modal, don't execute
      if ($drupalModal.attr('id') !== 'drupal-modal') {
        return;
      }

      // The actual modal and the rest of its contents won't exists
      // on the initial load. As such, we need to add a watcher to 
      // the DOM to find out when our dialog action buttons exist
      // so that we can act on them then.
      var observer = new MutationObserver(function (mutations) {
        mutations.forEach(function (mutation) {
          if (!mutation.addedNodes.length) {
            return
          }

          mutation.addedNodes.forEach(function (node) {
            var $node = $(node);
            if (!$node.hasClass('ui-dialog-buttonpane')) {
              return;
            }

            var $formSubmitButton = $('.form-submit', $form);
            var $dialogSubmitButton = $('.form-submit', $node);

            // Watch for our custom $.event from observeAttributes
            $formSubmitButton.on('attributeUpdated', function (e, attrData) {
              $dialogSubmitButton.attr(
                attrData.attributeName,
                attrData.attributeNewValue
              );
            })

            observer.disconnect();
          })
        })
      })

      observer.observe(document.body, {
        childList: true,
        subtree: true,
        attributes: false,
        characterData: false
      })
    },
    /**
     * Fires an event when an element's attributes change.
     *
     * @param $el
     *   The jQuery element being observed
     */
    observeAttributes: function ($el) {
      var observer = new MutationObserver(function (mutationList, observer) {
        var eventData = [];

        mutationList.forEach(function (mutation) {
          if (mutation.attributeName === 'style') {
            return;
          }

          var attributeName = (mutation.attributeName === 'class') ? 'classList' : mutation.attributeName;

          $el.trigger('attributeUpdated', {
            'attributeName': mutation.attributeName,
            'attributeNewValue': mutation.target[attributeName],
            'attributeOldValue': mutation.oldValue
          })
        })
      });

      observer.observe($el[0], {
        attributes: true,
        attributeOldValue: true,
      });
    },
  }
})(jQuery, Drupal, drupalSettings);