Index: trunk/bp-core/bp-core-template.php
===================================================================
--- trunk/bp-core/bp-core-template.php	(revision 6192)
+++ trunk/bp-core/bp-core-template.php	(working copy)
@@ -1511,7 +1511,8 @@
 }
 	function bp_get_the_body_class( $wp_classes, $custom_classes = false ) {
 
-		$bp_classes = array();
+		// observe WP custom background body class
+		$bp_classes = in_array( 'custom-background', $wp_classes ) ? array( 'custom-background' ) : array();
 
 		/** Pages *************************************************************/