Index: wp-admin/includes/list-table.php
===================================================================
--- wp-admin/includes/list-table.php	(revision 15893)
+++ wp-admin/includes/list-table.php	(working copy)
@@ -782,11 +782,15 @@
 		$this->display_rows();
 		$rows = ob_get_clean();
 
-		die( json_encode( array(
-			'rows' => $rows,
-			'total_items' => sprintf( _n( '1 item', '%s items', $total_items ), number_format_i18n( $total_items ) ),
-			'total_pages' => $total_pages
-		) ) );
+		$response = array( 'rows' => $rows );
+		
+		if( isset( $total_items ) )
+			$response['total_items'] = sprintf( _n( '1 item', '%s items', $total_items ), number_format_i18n( $total_items ) );
+			
+		if( isset( $total_pages ) )
+			$response['total_pages'] = $total_pages;
+			
+		die( json_encode( $response ) );
 	}
 
 	/**