diff --git a/core/model/Hierarchy.php b/core/model/Hierarchy.php
index 86ece4494..6059cc32f 100755
--- a/core/model/Hierarchy.php
+++ b/core/model/Hierarchy.php
@@ -670,6 +670,9 @@ class Hierarchy extends DataObjectDecorator {
 	function flushCache() {
 		$this->_cache_children = null;
 		$this->_cache_numChildren = null;
+		self::$marked = array();
+		self::$expanded = array();
+		self::$treeOpened = array();
 	}
 }