Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 20037)
+++ wp-includes/user.php	(working copy)
@@ -942,6 +942,7 @@
 
 	if ( 0 == $user->ID ) {
 		$user_login = $user_email = $user_url = $user_pass_md5 = $user_identity = '';
+		$userdata = null;
 		return;
 	}