Index: src/wp-includes/functions.php
===================================================================
--- src/wp-includes/functions.php	(revision 38828)
+++ src/wp-includes/functions.php	(working copy)
@@ -2868,7 +2868,7 @@
 	);
 	$r = wp_parse_args( $args, $defaults );
 
-	if ( ! headers_sent() ) {
+	if ( ! headers_sent() && ( 0 === ob_get_level() || 0 === ob_get_length() ) ) {
 		status_header( $r['response'] );
 	}
 	if ( is_scalar( $message ) )