Ticket #14554: 14554.diff

wp-includes/update.php

@@ -334 +334 @@
         wp_update_themes();
 }
 
+if ( ! is_main_site() )
+        return;
+
 add_action( 'admin_init', '_maybe_update_core' );
 add_action( 'wp_version_check', 'wp_version_check' );