Index: wp-includes/capabilities.php
===================================================================
--- wp-includes/capabilities.php	(revision 21256)
+++ wp-includes/capabilities.php	(working copy)
@@ -1380,7 +1380,7 @@
  * @return bool True if the user is a site admin.
  */
 function is_super_admin( $user_id = false ) {
-	if ( $user_id )
+	if ( $user_id && $user_id != get_current_user_id() )
 		$user = new WP_User( $user_id );
 	else
 		$user = wp_get_current_user();
Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 21256)
+++ wp-includes/pluggable.php	(working copy)
@@ -133,6 +133,9 @@
  * @return bool|object False on failure, WP_User object on success
  */
 function get_user_by( $field, $value ) {
+	if ( 'id' === $field && get_current_user_id() == $value )
+		return wp_get_current_user();
+
 	$userdata = WP_User::get_data_by( $field, $value );
 
 	if ( !$userdata )