diff --git a/core/includes/common.inc b/core/includes/common.inc
index 75dacc2..e50791f 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -6358,7 +6358,7 @@ function drupal_array_set_nested_value(array &$array, array $parents, $value, $f
  *
  * @see drupal_array_set_nested_value()
  */
-function drupal_array_get_nested_value(array &$array, array $parents, &$key_exists = NULL) {
+function &drupal_array_get_nested_value(array &$array, array $parents, &$key_exists = NULL) {
   $ref = &$array;
   foreach ($parents as $parent) {
     if (is_array($ref) && array_key_exists($parent, $ref)) {
@@ -6366,7 +6366,8 @@ function drupal_array_get_nested_value(array &$array, array $parents, &$key_exis
     }
     else {
       $key_exists = FALSE;
-      return NULL;
+      $null = NULL;
+      return $null;
     }
   }
   $key_exists = TRUE;
diff --git a/core/includes/form.inc b/core/includes/form.inc
index 00f9533..d077047 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -2124,30 +2124,13 @@ function form_state_values_clean(&$form_state) {
   foreach ($form_state['buttons'] as $button) {
     // Remove this button's value from the submitted form values by finding
     // the value corresponding to this button.
-    // We iterate over the #parents of this button and move a reference to
-    // each parent in $form_state['values']. For example, if #parents is:
-    //   array('foo', 'bar', 'baz')
-    // then the corresponding $form_state['values'] part will look like this:
-    // array(
-    //   'foo' => array(
-    //     'bar' => array(
-    //       'baz' => 'button_value',
-    //     ),
-    //   ),
-    // )
-    // We start by (re)moving 'baz' to $last_parent, so we are able unset it
-    // at the end of the iteration. Initially, $values will contain a
-    // reference to $form_state['values'], but in the iteration we move the
-    // reference to $form_state['values']['foo'], and finally to
-    // $form_state['values']['foo']['bar'], which is the level where we can
-    // unset 'baz' (that is stored in $last_parent).
     $parents = $button['#parents'];
-    $values = &$form_state['values'];
     $last_parent = array_pop($parents);
-    foreach ($parents as $parent) {
-      $values = &$values[$parent];
+    $key_exists = NULL;
+    $values = &drupal_array_get_nested_value($form_state['values'], $parents, $key_exists);
+    if ($key_exists && is_array($values)) {
+      unset($values[$last_parent]);
     }
-    unset($values[$last_parent]);
   }
 }
 
diff --git a/core/modules/simpletest/tests/form.test b/core/modules/simpletest/tests/form.test
index 1508f4c..70ebf86 100644
--- a/core/modules/simpletest/tests/form.test
+++ b/core/modules/simpletest/tests/form.test
@@ -545,7 +545,7 @@ class FormValidationTestCase extends DrupalWebTestCase {
    */
   function testValidateLimitErrors() {
     $edit = array(
-      'test' => 'invalid', 
+      'test' => 'invalid',
       'test_numeric_index[0]' => 'invalid',
       'test_substring[foo]' => 'invalid',
     );
@@ -1112,6 +1112,51 @@ class FormStateValuesCleanTestCase extends DrupalWebTestCase {
 }
 
 /**
+ * Tests $form_state clearance with form elements having buttons.
+ */
+class FormStateValuesCleanAdvancedTestCase extends DrupalWebTestCase {
+  /**
+   * An image file path for uploading.
+   */
+  protected $image;
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Form state values clearance (advanced)',
+      'description' => 'Test proper removal of submitted form values using form_state_values_clean() when having forms with elements containing buttons like "managed_file".',
+      'group' => 'Form API',
+    );
+  }
+
+  function setUp() {
+    parent::setUp('form_test');
+  }
+
+  /**
+   * Tests form_state_values_clean().
+   */
+  function testFormStateValuesCleanAdvanced() {
+
+    // Get an image for uploading.
+    $image_files = $this->drupalGetTestFiles('image');
+    $this->image = current($image_files);
+
+    // Check if the physical file is there.
+    $this->assertTrue(is_file($this->image->uri), t("The image file we're going to upload exists."));
+
+    // "Browse" for the desired file.
+    $edit = array('files[image]' => drupal_realpath($this->image->uri));
+
+    // Post the form.
+    $this->drupalPost('form_test/form-state-values-clean-advanced', $edit, t('Submit'));
+
+    // Expecting a 200 HTTP code.
+    $this->assertResponse(200, t('Received a 200 response for posted test file.'));
+    $this->assertRaw(t('You WIN!'), t('Found the success message.'));
+  }
+}
+
+/**
  * Tests form rebuilding.
  *
  * @todo Add tests for other aspects of form rebuilding.
diff --git a/core/modules/simpletest/tests/form_test.module b/core/modules/simpletest/tests/form_test.module
index 50b1c68..0393b18 100644
--- a/core/modules/simpletest/tests/form_test.module
+++ b/core/modules/simpletest/tests/form_test.module
@@ -92,6 +92,14 @@ function form_test_menu() {
     'type' => MENU_CALLBACK,
   );
 
+  $items['form_test/form-state-values-clean-advanced'] = array(
+    'title' => 'Form state values clearance advanced test',
+    'page callback' => 'drupal_get_form',
+    'page arguments' => array('form_test_form_state_values_clean_advanced_form'),
+    'access arguments' => array('access content'),
+    'type' => MENU_CALLBACK,
+  );
+
   $items['form-test/checkbox'] = array(
     'title' => t('Form test'),
     'page callback' => 'drupal_get_form',
@@ -803,6 +811,33 @@ function form_test_form_state_values_clean_form_submit($form, &$form_state) {
 }
 
 /**
+ * Form constructor for the form_state_values_clean() test.
+ */
+function form_test_form_state_values_clean_advanced_form($form, &$form_state) {
+  // Build an example form containing a managed file and a submit form element.
+  $form['image'] = array(
+    '#type' => 'managed_file',
+    '#title' => t('Image'),
+    '#upload_location' => 'public://',
+    '#default_value' => 0,
+  );
+  $form['submit'] = array(
+    '#type' => 'submit',
+    '#value' => t('Submit'),
+  );
+  return $form;
+}
+
+/**
+ * Form submission handler for form_test_form_state_values_clean_advanced_form().
+ */
+function form_test_form_state_values_clean_advanced_form_submit($form, &$form_state) {
+  form_state_values_clean($form_state);
+  print t('You WIN!');
+  exit;
+}
+
+/**
  * Build a form to test a checkbox.
  */
 function _form_test_checkbox($form, &$form_state) {