diff --git a/core/lib/Drupal/Core/Field/FieldItemList.php b/core/lib/Drupal/Core/Field/FieldItemList.php
index 4a034a8..249b59a 100644
--- a/core/lib/Drupal/Core/Field/FieldItemList.php
+++ b/core/lib/Drupal/Core/Field/FieldItemList.php
@@ -43,11 +43,16 @@ class FieldItemList extends ItemList implements FieldItemListInterface {
    */
   public function __construct(DataDefinitionInterface $definition, $name = NULL, TypedDataInterface $parent = NULL) {
     parent::__construct($definition, $name, $parent);
-    // Always initialize one empty item as most times a value for at least one
-    // item will be present. That way prototypes created by
-    // \Drupal\Core\TypedData\TypedDataManager::getPropertyInstance() will
-    // already have this field item ready for use after cloning.
-    $this->list[0] = $this->createItem(0);
+
+    // Let computed feilds run.
+    // @todo There's probably an issue with computed fields - there's no way
+    // isEmpty() / filterEmptyItems() can work reliably on those ?
+    if ($definition->isComputed() || $definition->getItemDefinition()->isComputed()) {
+      // @todo be smarter with appendItem() ?
+      // Should appendItem() check that the item is not empty ?
+      $item = $this->createItem(0);
+      $this->list[0] = $item;
+    }
   }
 
   /**
@@ -222,7 +227,7 @@ public function applyDefaultValue($notify = TRUE) {
     // are valid default values.
     if (!isset($value) || (is_array($value) && empty($value))) {
       // Create one field item and apply defaults.
-      $this->offsetGet(0)->applyDefaultValue(FALSE);
+//      $this->offsetGet(0)->applyDefaultValue(FALSE);
     }
     else {
       $this->setValue($value, $notify);
diff --git a/core/modules/comment/lib/Drupal/comment/CommentFormController.php b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
index 3f88b51..73970cd 100644
--- a/core/modules/comment/lib/Drupal/comment/CommentFormController.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
@@ -218,7 +218,10 @@ public function form(array $form, array &$form_state) {
     // Add internal comment properties.
     $original = $comment->getUntranslated();
     foreach (array('cid', 'pid', 'entity_id', 'entity_type', 'field_id', 'uid', 'langcode') as $key) {
-      $key_name = key($comment->$key->offsetGet(0)->getPropertyDefinitions());
+      // @todo No need for an item to get the propertyDefinition after
+      // https://drupal.org/node/2002134
+      $item = $comment->$key->offsetExists(0) ? $comment->$key->offsetGet(0) : $comment->$key->appendItem();
+      $key_name = key($item->getPropertyDefinitions());
       $form[$key] = array('#type' => 'value', '#value' => $original->$key->{$key_name});
     }