Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.1287
diff -u -p -r1.1287 common.inc
--- includes/common.inc	9 Feb 2011 02:23:52 -0000	1.1287
+++ includes/common.inc	17 Feb 2011 20:57:53 -0000
@@ -5568,9 +5568,9 @@ function drupal_render(&$elements) {
     return $cached_output;
   }
 
-  // If #markup is not empty, set #type. This allows to specify just #markup on
-  // an element without setting #type.
-  if (!empty($elements['#markup']) && !isset($elements['#type'])) {
+  // If #markup is set, ensure #type is set. This allows to specify just #markup
+  // on an element without setting #type.
+  if (isset($elements['#markup']) && !isset($elements['#type'])) {
     $elements['#type'] = 'markup';
   }