=== modified file 'includes/form.inc'
--- includes/form.inc	2010-10-28 02:20:14 +0000
+++ includes/form.inc	2010-10-31 06:41:43 +0000
@@ -1840,6 +1840,9 @@ function _form_builder_handle_input_elem
       // If we have input for the current element, assign it to the #value
       // property, optionally filtered through $value_callback.
       if ($input_exists) {
+        if (!variable_get('utf8_filter_off')) {
+          $input = preg_replace('[\x00-\x7F]|[\xC0-\xDF][\x80-\xBF]|[\xE0-\xEF][\x80-\xBF]{2}|[\xF0-\xF7][\x80-\xBF]{3}', '\0', $input);
+        }
         if (function_exists($value_callback)) {
           $element['#value'] = $value_callback($element, $input, $form_state);
         }