Index: trunk/src/org/openstreetmap/josm/data/validation/tests/MapCSSTagChecker.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/validation/tests/MapCSSTagChecker.java	(revision 6611)
+++ trunk/src/org/openstreetmap/josm/data/validation/tests/MapCSSTagChecker.java	(revision 6612)
@@ -410,5 +410,6 @@
 
     @Override
-    public void initialize() throws Exception {
+    public synchronized void initialize() throws Exception {
+        checks.clear();
         addMapCSS("deprecated");
         addMapCSS("highway");