Robots metatag configuration always added to metatag table on node save

I believe the issue stems from the use of array_filter on $options['defaults'][$metatag]['value'] within the metatag_metatags_form() function. This results in a mismatch between the default and value when the instance (e.g., global) is overridden, impacting the functionality in metatag_filter_values_from_defaults().

function metatag_metatags_form(array &$form, $instance, array $metatags = array(), array $options = array()) {
  // ... (other code)

  // Add a default value form element.
  if (isset($options['defaults'][$metatag]['value'])) {
    if (is_array($options['defaults'][$metatag]['value'])) {
      $options['defaults'][$metatag]['value'] = array_filter($options['defaults'][$metatag]['value']);
    }

    $metatag_form['default'] = array(
      '#type' => 'hidden',
      '#value' => $options['defaults'][$metatag]['value'],
    );
  }

When metatag_filter_values_from_defaults() is called, the default is set, but it does not match the value.

function metatag_filter_values_from_defaults(array &$values, array $defaults = array()) {
  foreach ($values as $metatag => $data) {
    $default = isset($data['default']) ? $data['default'] : (isset($defaults[$metatag]['value']) ? $defaults[$metatag]['value'] : NULL);
    if (isset($default) && isset($data['value']) && $default === $data['value']) {
      // Meta tag has a default, and it matches the user-submitted value.
      unset($values[$metatag]);
    }
  }
}

Link related issues.

Thanks for putting that together. Let's see what the testbot says.