There is absolutely no need to specify class name (it will validate anyway).
diff --git a/system/helpers/form_helper.php b/system/helpers/form_helper.php
index acd75c2..bca0ff0 100644
--- a/system/helpers/form_helper.php
+++ b/system/helpers/form_helper.php
@@ -72,7 +72,7 @@
 
 		if (is_array($hidden) AND count($hidden) > 0)
 		{
-			$form .= sprintf("\n<div class=\"hidden\">%s</div>", form_hidden($hidden));
+			$form .= sprintf("\n<div>%s</div>", form_hidden($hidden));
 		}
 
 		return $form;
@@ -1053,4 +1053,4 @@
 
 
 /* End of file form_helper.php */
-/* Location: ./system/helpers/form_helper.php */
\ No newline at end of file
+/* Location: ./system/helpers/form_helper.php */