--- wp-admin/includes/dashboard.php	2010-08-15 12:23:19.000000000 +0100
+++ dashboard.php	2010-08-15 12:19:31.000000000 +0100
@@ -764,7 +764,7 @@
 			$text = __( '%1$s linked here saying, "%3$s"' );
 
 		if ( $show_date ) {
-			if ( $show_author || $show_summary )
+			if ( isset( $show_author ) || isset( $show_summary ) )
 				/* translators: incoming links feed, %4$s is the date */
 				$text .= ' ' . __( 'on %4$s' );
 			$date = esc_html( strip_tags( $item->get_date() ) );