Ticket #20137: 20137.patch

wp-includes/customize-controls.php

@@ -80 +80 @@
 
         do_action( 'customize_controls_print_footer_scripts' );
 
+        // Check current scheme and load the preview with the same scheme
+        $scheme = is_ssl() ? 'https' : 'http';
         $settings = array(
-                'preview' => esc_url( home_url( '/' ) ),
+                'preview' => esc_url( get_home_url( null, '/', $scheme ) ),
                 'values'  => array(),
                 'prefix'  => WP_Customize_Setting::name_prefix,
         );