Index: wp-admin/async-upload.php
===================================================================
--- wp-admin/async-upload.php	(revision 19578)
+++ wp-admin/async-upload.php	(working copy)
@@ -23,7 +23,7 @@
 unset($current_user);
 require_once('./admin.php');
 
-header('Content-Type: text/plain; charset=' . get_option('blog_charset'));
+header('Content-Type: text/html; charset=' . get_option('blog_charset'));
 
 if ( !current_user_can('upload_files') )
 	wp_die(__('You do not have permission to upload files.'));