diff --git a/core/model/Hierarchy.php b/core/model/Hierarchy.php
index f45fc6b7e..4e5b8a444 100755
--- a/core/model/Hierarchy.php
+++ b/core/model/Hierarchy.php
@@ -668,6 +668,12 @@ class Hierarchy extends DataObjectDecorator {
 		$this->_cache_allChildren = null;
 		$this->_cache_numChildren = null;
 	}
+	
+	function reset() {
+		self::$marked = array();
+		self::$expanded = array();
+		self::$treeOpened = array();
+	}
 }
 
 ?>
diff --git a/dev/SapphireTest.php b/dev/SapphireTest.php
index 915203040..97fe7e68e 100755
--- a/dev/SapphireTest.php
+++ b/dev/SapphireTest.php
@@ -71,6 +71,7 @@ class SapphireTest extends PHPUnit_Framework_TestCase {
 		Versioned::reset();
 		DataObject::reset();
 		SiteTree::reset();
+		Hierarchy::reset();
 		Controller::curr()->setSession(new Session(array()));
 
 		$className = get_class($this);