diff --git modules/field/field.attach.inc modules/field/field.attach.inc
index 7434dda..2d274a5 100644
--- modules/field/field.attach.inc
+++ modules/field/field.attach.inc
@@ -1036,10 +1036,17 @@ function field_attach_delete_revision($entity_type, $entity) {
 /**
  * Prepare field data prior to display.
  *
- * This function must be called before field_attach_view(). It lets field
- * types and formatters load additional data needed for display, and
- * therefore accepts an array of entities to allow query optimisation when
- * displaying lists of entities.
+ * This function lets field types and formatters load additional data
+ * needed for display that is not automatically loaded during
+ * field_attach_load(). It accepts an array of entities to allow query
+ * optimisation when displaying lists of entities.
+ *
+ * field_attach_prepare_view() and field_attach_view() are two halves
+ * of the same operation. It is safe to call
+ * field_attach_prepare_view() multiple times on the same entity
+ * before calling field_attach_view() on it, but calling any Field
+ * API operation on an entity between passing that entity to these two
+ * functions may yield incorrect results.
  *
  * @param $entity_type
  *   The type of $entities; e.g. 'node' or 'user'.
@@ -1077,8 +1084,12 @@ function field_attach_prepare_view($entity_type, $entities, $view_mode) {
  * Each field is displayed according to the display options specified in the
  * $instance definition for the given $view_mode.
  *
- * The entity must have run through field_attach_prepare_view() beforehands.
- * @see field_attach_prepare_view()
+ * field_attach_prepare_view() and field_attach_view() are two halves
+ * of the same operation. It is safe to call
+ * field_attach_prepare_view() multiple times on the same entity
+ * before calling field_attach_view() on it, but calling any Field
+ * API operation on an entity between passing that entity to these two
+ * functions may yield incorrect results.
  *
  * Sample structure:
  * @code
diff --git modules/node/node.pages.inc modules/node/node.pages.inc
index c5a8307..285dd58 100644
--- modules/node/node.pages.inc
+++ modules/node/node.pages.inc
@@ -315,6 +315,9 @@ function node_form_build_preview($form, &$form_state) {
  */
 function node_preview($node) {
   if (node_access('create', $node) || node_access('update', $node)) {
+    // Previewing alters $node so it needs to be cloned.
+    $node = clone $node;
+
     _field_invoke_multiple('load', 'node', array($node->nid => $node));
     // Load the user's name when needed.
     if (isset($node->name)) {
@@ -339,11 +342,9 @@ function node_preview($node) {
     field_attach_prepare_view('node', $nodes, 'full');
 
     // Display a preview of the node.
-    // Previewing alters $node so it needs to be cloned.
     if (!form_get_errors()) {
-      $cloned_node = clone $node;
-      $cloned_node->in_preview = TRUE;
-      $output = theme('node_preview', array('node' => $cloned_node));
+      $node->in_preview = TRUE;
+      $output = theme('node_preview', array('node' => $node));
     }
     drupal_set_title(t('Preview'), PASS_THROUGH);
 
diff --git modules/node/node.test modules/node/node.test
index 1e5d539..0574b90 100644
--- modules/node/node.test
+++ modules/node/node.test
@@ -387,6 +387,16 @@ class PagePreviewTestCase extends DrupalWebTestCase {
   }
 
   /**
+   * Create a node, preview it, and make sure the node is unchanged.
+   */
+  function testPagePreviewNodeEqual() {
+    $node = $this->drupalCreateNode();
+    $before = clone $node;
+    node_preview($node);
+    $this->assertTrue($node == $before, 'Node unchanged by preview.')
+   }  
+
+  /**
    * Check the node preview functionality, when using revisions.
    */
   function testPagePreviewWithRevisions() {