Index: wp-includes/plugin.php
===================================================================
--- wp-includes/plugin.php	(revision 14524)
+++ wp-includes/plugin.php	(working copy)
@@ -737,7 +737,9 @@
 	if ( is_string($function) )
 		return $function;
 
-	$function = (array) $function;
+	// Closure
+	if ( is_object($function) )
+		return spl_object_hash($function);
 
 	if (is_object($function[0]) ) {
 		// Object Class Calling