--- a/compiler/PPCContext.st	Wed Nov 05 21:40:01 2014 +0000
+++ b/compiler/PPCContext.st	Wed Nov 05 23:05:19 2014 +0000
@@ -268,8 +268,16 @@
 !
 
 restoreProperties: aPPContextMemento
+	properties ifNil: [ ^ self ].
+	
+	properties keysDo: [ :key |
+		(aPPContextMemento hasProperty: key)
+			ifTrue: [ properties at: key put: (aPPContextMemento propertyAt: key) ]
+			ifFalse: [ properties removeKey: key  ]. 
+	].
+
 	aPPContextMemento keysAndValuesDo: [ :key :value |
-		self propertyAt: key put: value
-	].
+		properties at: key put: value
+	]
 ! !