Index: includes/form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.511
diff -u -p -r1.511 form.inc
--- includes/form.inc	17 Nov 2010 04:10:51 -0000	1.511
+++ includes/form.inc	22 Nov 2010 03:39:56 -0000
@@ -1858,6 +1858,10 @@ function _form_builder_handle_input_elem
         drupal_array_set_nested_value($form_state['input'], $element['#parents'], NULL);
         $input_exists = TRUE;
       }
+      // Check whether the input is valid UTF-8.
+      if ($input_exists && variable_get('form_filter_utf8', TRUE) && !drupal_validate_utf8($input)) {
+        $input_exists = FALSE;
+      }
       // If we have input for the current element, assign it to the #value
       // property, optionally filtered through $value_callback.
       if ($input_exists) {