Ticket #29234: 29234.patch

src/wp-admin/includes/class-wp-upgrader.php

@@ -1045 +1045 @@
                                 'destination' => get_theme_root( $theme ),
                                 'clear_destination' => true,
                                 'clear_working' => true,
+                                'is_multi' => true,
                                 'hook_extra' => array(
                                         'theme' => $theme
                                 ),