Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.1248
diff -u -p -r1.1248 common.inc
--- includes/common.inc	5 Nov 2010 01:29:20 -0000	1.1248
+++ includes/common.inc	5 Nov 2010 19:57:31 -0000
@@ -5956,14 +5956,22 @@ function element_set_attributes(array &$
  *   An array of parent keys, starting with the outermost key.
  * @param $value
  *   The value to set.
+ * @param $force
+ *   (Optional) If TRUE, the value is forced into the structure even if it
+ *   requires the deletion of an already existing non-array parent value. If
+ *   FALSE, PHP throws an error if trying to add into a value that is not an
+ *   array. Defaults to FALSE.
  *
  * @see drupal_array_get_nested_value()
  */
-function drupal_array_set_nested_value(array &$array, array $parents, $value) {
+function drupal_array_set_nested_value(array &$array, array $parents, $value, $force = FALSE) {
   $ref = &$array;
   foreach ($parents as $parent) {
-    // Note that PHP is fine with referencing a not existing array key - in this
-    // case it just creates an entry with NULL as value.
+    // PHP auto-creates container arrays and NULL entries without error if $ref
+    // is NULL, but throws an error if $ref is set, but not an array.
+    if ($force && isset($ref) && !is_array($ref)) {
+      $ref = array();
+    }
     $ref = &$ref[$parent];
   }
   $ref = $value;
@@ -6027,10 +6035,7 @@ function drupal_array_set_nested_value(a
 function drupal_array_get_nested_value(array &$array, array $parents, &$key_exists = NULL) {
   $ref = &$array;
   foreach ($parents as $parent) {
-    // array_key_exists() is slower than isset() and triggers notices if the
-    // second argument is not an array, so only call it when absolutely
-    // necessary.
-    if (isset($ref[$parent]) || (is_array($ref) && array_key_exists($parent, $ref))) {
+    if (is_array($ref) && array_key_exists($parent, $ref)) {
       $ref = &$ref[$parent];
     }
     else {
Index: includes/form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.507
diff -u -p -r1.507 form.inc
--- includes/form.inc	28 Oct 2010 02:20:14 -0000	1.507
+++ includes/form.inc	5 Nov 2010 19:57:32 -0000
@@ -1031,10 +1031,29 @@ function drupal_validate_form($form_id, 
         drupal_array_set_nested_value($values, $section, $value);
       }
     }
-    // For convenience we always make the value of the pressed button available.
+    // A button's #value does not require validation, so for convenience we
+    // allow the value of the clicked button to be retained in its normal
+    // $form_state['values'] locations, even if these locations are not included
+    // in #limit_validation_errors.
     if (isset($form_state['triggering_element']['#button_type'])) {
-      $values[$form_state['triggering_element']['#name']] = $form_state['triggering_element']['#value'];
-      drupal_array_set_nested_value($values, $form_state['triggering_element']['#parents'], $form_state['triggering_element']['#value']);
+      $button_value = $form_state['triggering_element']['#value'];
+
+      // Like all input controls, the button value may be in the location
+      // dictated by #parents. If it is, copy it to $values, but do not override
+      // what may already be in $values.
+      $parents = $form_state['triggering_element']['#parents'];
+      if (!drupal_array_nested_key_exists($values, $parents) && drupal_array_get_nested_value($form_state['values'], $parents) === $button_value) {
+        drupal_array_set_nested_value($values, $parents, $button_value);
+      }
+
+      // Additionally, form_builder() places the button value in
+      // $form_state['values'][BUTTON_NAME]. If it's still there, after
+      // validation handlers have run, copy it to $values, but do not override
+      // what may already be in $values.
+      $name = $form_state['triggering_element']['#name'];
+      if (!isset($values[$name]) && isset($form_state['values'][$name]) && $form_state['values'][$name] === $button_value) {
+        $values[$name] = $button_value;
+      }
     }
     $form_state['values'] = $values;
   }
@@ -2301,7 +2320,7 @@ function form_type_token_value($element,
  *   Form state array where the value change should be recorded.
  */
 function form_set_value($element, $value, &$form_state) {
-  drupal_array_set_nested_value($form_state['values'], $element['#parents'], $value);
+  drupal_array_set_nested_value($form_state['values'], $element['#parents'], $value, TRUE);
 }
 
 /**
Index: modules/file/file.field.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/file/file.field.inc,v
retrieving revision 1.38
diff -u -p -r1.38 file.field.inc
--- modules/file/file.field.inc	31 Oct 2010 12:12:00 -0000	1.38
+++ modules/file/file.field.inc	5 Nov 2010 19:57:34 -0000
@@ -648,8 +648,9 @@ function file_field_widget_process($elem
   // Adjust the AJAX settings so that on upload and remove of any individual
   // file, the entire group of file fields is updated together.
   if ($field['cardinality'] != 1) {
-    $new_path = preg_replace('/\/\d+\//', '/', $element['remove_button']['#ajax']['path'], 1);
-    $field_element = drupal_array_get_nested_value($form, array_slice($element['#array_parents'], 0, -1));
+    $parents = array_slice($element['#array_parents'], 0, -1);
+    $new_path = 'file/ajax/' . implode('/', $parents) . '/' . $form['form_build_id']['#value'];
+    $field_element = drupal_array_get_nested_value($form, $parents);
     $new_wrapper = $field_element['#id'] . '-ajax-wrapper';
     foreach (element_children($element) as $key) {
       if (isset($element[$key]['#ajax'])) {
Index: modules/file/file.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/file/file.module,v
retrieving revision 1.45
diff -u -p -r1.45 file.module
--- modules/file/file.module	20 Oct 2010 15:22:53 -0000	1.45
+++ modules/file/file.module	5 Nov 2010 19:57:35 -0000
@@ -360,7 +360,7 @@ function file_managed_file_process($elem
   $element['#tree'] = TRUE;
 
   $ajax_settings = array(
-    'path' => 'file/ajax/' . implode('/', $element['#parents']) . '/' . $form['form_build_id']['#value'],
+    'path' => 'file/ajax/' . implode('/', $element['#array_parents']) . '/' . $form['form_build_id']['#value'],
     'wrapper' => $element['#id'] . '-ajax-wrapper',
     'effect' => 'fade',
     'progress' => array(