--- FreeformEvaluator.java	
+++ FreeformEvaluator.java	
@@ -92,14 +92,15 @@ 
     }
     
     private PropertyEvaluator initEval() throws IOException {
+        PropertyProvider preprovider = project.helper().getStockPropertyPreprovider();
+        List<PropertyProvider> defs = new ArrayList<PropertyProvider>();
+        synchronized (intermediateEvaluators) {
         // Stop listening to old intermediate evaluators.
         Iterator<PropertyEvaluator> ieIt = intermediateEvaluators.iterator();
         while (ieIt.hasNext()) {
             ieIt.next().removePropertyChangeListener(this);
             ieIt.remove();
         }
-        PropertyProvider preprovider = project.helper().getStockPropertyPreprovider();
-        List<PropertyProvider> defs = new ArrayList<PropertyProvider>();
         Element genldata = project.getPrimaryConfigurationData();
         Element properties = Util.findElement(genldata, "properties", FreeformProjectType.NS_GENERAL); // NOI18N
         if (properties != null) {
@@ -125,6 +126,7 @@ 
                 }
             }
         }
+        }
         return PropertyUtils.sequentialPropertyEvaluator(preprovider, defs.toArray(new PropertyProvider[defs.size()]));
     }
     
@@ -173,7 +175,11 @@ 
     public void propertyChange(PropertyChangeEvent propertyChangeEvent) {
         Object source = propertyChangeEvent.getSource();
         assert source instanceof PropertyEvaluator : source;
-        if (intermediateEvaluators.contains(source)) {
+        boolean contains;
+        synchronized (intermediateEvaluators) {
+            contains = intermediateEvaluators.contains(source);
+        }
+        if (contains) {
             // A <property-file> may have changed location. Generally need to rebuild the list of definers.
             fireAnyChange();
         } else {