diff --git a/core/lib/Drupal/Core/Entity/EntityForm.php b/core/lib/Drupal/Core/Entity/EntityForm.php
index fb015c7..088d6af 100644
--- a/core/lib/Drupal/Core/Entity/EntityForm.php
+++ b/core/lib/Drupal/Core/Entity/EntityForm.php
@@ -165,7 +165,7 @@ public function processForm($element, FormStateInterface $form_state, $form) {
   public function afterBuild(array $element, FormStateInterface $form_state) {
     // Rebuild the entity if #after_build is being called as part of a form
     // rebuild, i.e. if we are processing input.
-    if ($form_state->isProcessingInput()) {
+    if ($form_state->isRebuilding() && $form_state->isProcessingInput()) {
       $this->entity = $this->buildEntity($element, $form_state);
     }
 
diff --git a/core/modules/content_translation/content_translation.module b/core/modules/content_translation/content_translation.module
index 93d73f9..474af56 100644
--- a/core/modules/content_translation/content_translation.module
+++ b/core/modules/content_translation/content_translation.module
@@ -318,13 +318,13 @@ function content_translation_entity_extra_field_info() {
 }
 
 /**
- * Implements hook_form_FORM_ID_alter() for 'field_ui_field_edit_form'.
+ * Implements hook_form_FORM_ID_alter() for 'field_config_edit_form'.
  */
-function content_translation_form_field_ui_field_edit_form_alter(array &$form, FormStateInterface $form_state) {
-  $field = $form_state->get('field');
+function content_translation_form_field_config_edit_form_alter(array &$form, FormStateInterface $form_state) {
+  $field = $form_state->getFormObject()->getEntity();
   $bundle_is_translatable = \Drupal::service('content_translation.manager')->isEnabled($field->entity_type, $field->bundle);
 
-  $form['field']['translatable'] = array(
+  $form['translatable'] = array(
     '#type' => 'checkbox',
     '#title' => t('Users may translate this field'),
     '#default_value' => $field->isTranslatable(),
@@ -338,7 +338,7 @@ function content_translation_form_field_ui_field_edit_form_alter(array &$form, F
     $toggle_url = \Drupal::url('language.content_settings_page', array(), array(
       'query' => drupal_get_destination(),
     ));
-    $form['field']['translatable']['#description'] = t('To configure translation for this field, <a href="@language-settings-url">enable language support</a> for this type.', array(
+    $form['translatable']['#description'] = t('To configure translation for this field, <a href="@language-settings-url">enable language support</a> for this type.', array(
       '@language-settings-url' => $toggle_url,
     ));
   }
@@ -347,8 +347,8 @@ function content_translation_form_field_ui_field_edit_form_alter(array &$form, F
     module_load_include('inc', 'content_translation', 'content_translation.admin');
     $element = content_translation_field_sync_widget($field);
     if ($element) {
-      $form['field']['third_party_settings']['content_translation']['translation_sync'] = $element;
-      $form['field']['third_party_settings']['content_translation']['translation_sync']['#weight'] = -10;
+      $form['third_party_settings']['content_translation']['translation_sync'] = $element;
+      $form['third_party_settings']['content_translation']['translation_sync']['#weight'] = -10;
     }
   }
 }
diff --git a/core/modules/content_translation/src/Tests/ContentTranslationSettingsTest.php b/core/modules/content_translation/src/Tests/ContentTranslationSettingsTest.php
index 9874574..4fc4094 100644
--- a/core/modules/content_translation/src/Tests/ContentTranslationSettingsTest.php
+++ b/core/modules/content_translation/src/Tests/ContentTranslationSettingsTest.php
@@ -174,7 +174,7 @@ function testSettingsUI() {
 
       // Test that also the Field UI form behaves correctly.
       $translatable = !$translatable;
-      $edit = array('field[translatable]' => $translatable);
+      $edit = array('translatable' => $translatable);
       $this->drupalPostForm('admin/structure/types/manage/article/fields/node.article.body', $edit, t('Save settings'));
       \Drupal::entityManager()->clearCachedFieldDefinitions();
       $field = FieldConfig::loadByName('node', 'article', 'body');
@@ -242,7 +242,7 @@ function testFieldTranslatableSettingsUI() {
     // translatable.
     $path = 'admin/structure/types/manage/article/fields/node.article.field_article_text';
     $this->drupalGet($path);
-    $this->assertFieldByXPath('//input[@id="edit-field-translatable" and @disabled="disabled"]');
+    $this->assertFieldByXPath('//input[@id="edit-translatable" and @disabled="disabled"]');
     $this->assertText('To configure translation for this field, enable language support for this type.', 'No translatable setting for field.');
 
     // Tests that field has translatable setting if bundle is translatable.
@@ -255,7 +255,7 @@ function testFieldTranslatableSettingsUI() {
     );
     $this->assertSettings('node', 'article', TRUE, $edit);
     $this->drupalGet($path);
-    $this->assertFieldByXPath('//input[@id="edit-field-translatable" and not(@disabled) and @checked="checked"]');
+    $this->assertFieldByXPath('//input[@id="edit-translatable" and not(@disabled) and @checked="checked"]');
     $this->assertNoText('To enable translation of this field, enable language support for this type.', 'Translatable setting for field available.');
   }
 
diff --git a/core/modules/content_translation/src/Tests/ContentTranslationSyncImageTest.php b/core/modules/content_translation/src/Tests/ContentTranslationSyncImageTest.php
index cbae0d4..f1b7688 100644
--- a/core/modules/content_translation/src/Tests/ContentTranslationSyncImageTest.php
+++ b/core/modules/content_translation/src/Tests/ContentTranslationSyncImageTest.php
@@ -88,11 +88,11 @@ function testImageFieldSync() {
     // Check that the alt and title fields are enabled for the image field.
     $this->drupalLogin($this->editor);
     $this->drupalGet('entity_test_mul/structure/' . $this->entityTypeId . '/fields/' . $this->entityTypeId . '.' . $this->entityTypeId . '.' . $this->fieldName);
-    $this->assertFieldChecked('edit-field-third-party-settings-content-translation-translation-sync-alt');
-    $this->assertFieldChecked('edit-field-third-party-settings-content-translation-translation-sync-title');
+    $this->assertFieldChecked('edit-third-party-settings-content-translation-translation-sync-alt');
+    $this->assertFieldChecked('edit-third-party-settings-content-translation-translation-sync-title');
     $edit = array(
-      'field[third_party_settings][content_translation][translation_sync][alt]' => FALSE,
-      'field[third_party_settings][content_translation][translation_sync][title]' => FALSE,
+      'third_party_settings[content_translation][translation_sync][alt]' => FALSE,
+      'third_party_settings[content_translation][translation_sync][title]' => FALSE,
     );
     $this->drupalPostForm(NULL, $edit, t('Save settings'));
 
diff --git a/core/modules/field_ui/src/Form/FieldConfigEditForm.php b/core/modules/field_ui/src/Form/FieldConfigEditForm.php
index c1542f1..8ee3a26 100644
--- a/core/modules/field_ui/src/Form/FieldConfigEditForm.php
+++ b/core/modules/field_ui/src/Form/FieldConfigEditForm.php
@@ -76,21 +76,23 @@ public function form(array $form, FormStateInterface $form_state) {
       '#weight' => -5,
     );
 
-    // Add field settings for the field type and a container for third party
-    // settings that modules can add to via hook_form_FORM_ID_alter().
     // Create an arbitrary entity object (used by the 'default value' widget).
     $ids = (object) array('entity_type' => $this->entity->getTargetEntityTypeId(), 'bundle' => $this->entity->bundle, 'entity_id' => NULL);
     $form['#entity'] = _field_create_entity_from_ids($ids);
     $items = $form['#entity']->get($this->entity->getName());
     $item = $items->first() ?: $items->appendItem();
 
+    // Add field settings for the field type and a container for third party
+    // settings that modules can add to via hook_form_FORM_ID_alter().
     $form['settings'] = array(
       '#tree' => TRUE,
       '#weight' => 10,
     );
     $form['settings'] += $item->fieldSettingsForm($form, $form_state);
-    $form['third_party_settings'] = array();
-    $form['third_party_settings']['#weight'] = 11;
+    $form['third_party_settings'] = array(
+      '#tree' => TRUE,
+      '#weight' => 11,
+    );
 
     // Add handling for default value.
     if ($element = $items->defaultValuesForm($form, $form_state)) {
@@ -98,6 +100,7 @@ public function form(array $form, FormStateInterface $form_state) {
         '#type' => 'details',
         '#title' => $this->t('Default value'),
         '#open' => TRUE,
+        '#tree' => TRUE,
         '#description' => $this->t('The default value for this field, used when creating new content.'),
       ));
 
diff --git a/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php b/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php
index b7d4350..215794a 100644
--- a/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php
+++ b/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php
@@ -293,7 +293,7 @@ public function testDefaultImages() {
     );
 
     $non_image = $this->drupalGetTestFiles('text');
-    $this->drupalPostForm(NULL, array('files[field_settings_default_image_uuid]' => drupal_realpath($non_image[0]->uri)), t("Upload"));
+    $this->drupalPostForm(NULL, array('files[settings_default_image_uuid]' => drupal_realpath($non_image[0]->uri)), t("Upload"));
     $this->assertText(t('The specified file text-0.txt could not be uploaded. Only files with the following extensions are allowed: png gif jpg jpeg.'), 'Non-image file cannot be used as default image.');
 
     // Confirm the default image is shown on the node form.
diff --git a/core/modules/link/src/Tests/LinkFieldUITest.php b/core/modules/link/src/Tests/LinkFieldUITest.php
index 97fd9c8..d9531ce 100644
--- a/core/modules/link/src/Tests/LinkFieldUITest.php
+++ b/core/modules/link/src/Tests/LinkFieldUITest.php
@@ -85,7 +85,7 @@ function testFieldUI() {
     // external only links.
     $label = $this->randomMachineName();
     $field_name = Unicode::strtolower($label);
-    $field_edit = ['field[settings][link_type]' => LinkItemInterface::LINK_EXTERNAL];
+    $field_edit = ['settings[link_type]' => LinkItemInterface::LINK_EXTERNAL];
     $this->fieldUIAddNewField($type_path, $field_name, $label, 'link', array(), $field_edit);
 
     // Test the help text displays when link allows only external links.