Index: wp-includes/post-template.php
===================================================================
--- wp-includes/post-template.php	(revision 21050)
+++ wp-includes/post-template.php	(working copy)
@@ -501,7 +501,7 @@
 	if ( is_admin_bar_showing() )
 		$classes[] = 'admin-bar';
 
-	if ( get_background_color() || get_theme_mod( 'background_image' ) || get_theme_support( 'custom-background', 'default-image' ) )
+	if ( get_theme_mod( 'background_color' ) || get_background_image() || current_theme_supports( 'custom-background', 'default-image' ) )
 		$classes[] = 'custom-background';
 
 	$page = $wp_query->get( 'page' );