Index: wp-includes/post-template.php
===================================================================
--- wp-includes/post-template.php	(revision 23644)
+++ wp-includes/post-template.php	(working copy)
@@ -501,7 +501,8 @@
 		}
 		if ( is_page_template() ) {
 			$classes[] = 'page-template';
-			$classes[] = 'page-template-' . sanitize_html_class( str_replace( '.', '-', get_page_template_slug( $page_id ) ) );
+			foreach ( explode( '/', get_page_template_slug( $page_id ) ) as $slug ) 
+				$classes[] = 'page-template-' . sanitize_html_class( str_replace( '.', '-', $slug ) );
 		} else {
 			$classes[] = 'page-template-default';
 		}