Index: src/wp-includes/js/wp-custom-header.js
===================================================================
--- src/wp-includes/js/wp-custom-header.js	(revision 39562)
+++ src/wp-includes/js/wp-custom-header.js	(working copy)
@@ -54,7 +54,8 @@
 					var handler = this.handlers[ id ];
 
 					if ( 'test' in handler && handler.test( settings ) ) {
-						this.activeHandler = handler.initialize.call( handler, settings );
+						this.activeHandler = handler;
+						handler.initialize.call( handler, settings );
 
 						// Dispatch custom event when the video is loaded.
 						trigger( document, 'wp-custom-header-video-loaded' );