Index: wp-includes/theme.php
===================================================================
--- wp-includes/theme.php	(revision 21049)
+++ wp-includes/theme.php	(working copy)
@@ -1102,8 +1102,8 @@
  * @access protected
  */
 function _custom_background_cb() {
-	// $background is the saved custom image, or the default image.
-	$background = get_background_image();
+	// $background is the saved custom image
+	$background = get_theme_mod( 'background_image' );
 
 	// $color is the saved custom color.
 	// A default has to be specified in style.css. It will not be printed here.
@@ -1677,4 +1677,4 @@
 		}());
 	</script>
 	<?php
-}
\ No newline at end of file
+}
Index: wp-includes/post-template.php
===================================================================
--- wp-includes/post-template.php	(revision 21049)
+++ 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_theme_mod( 'background_image' ) || get_theme_support( 'custom-background', 'default-image' ) )
 		$classes[] = 'custom-background';
 
 	$page = $wp_query->get( 'page' );