Index: wp-includes/plugin.php
===================================================================
--- wp-includes/plugin.php	(revision 11745)
+++ wp-includes/plugin.php	(working copy)
@@ -678,6 +678,11 @@
 	// If function then just skip all of the tests and not overwrite the following.
 	if ( is_string($function) )
 		return $function;
+	
+	// Closure Calling
+	if ( is_a($function, 'Closure') )
+		return spl_object_hash($function);
+
 	// Object Class Calling
 	else if (is_object($function[0]) ) {
 		$obj_idx = get_class($function[0]).$function[1];