Index: src/main/org/apache/tools/ant/util/IdentityStack.java
===================================================================
--- src/main/org/apache/tools/ant/util/IdentityStack.java	(revision 1380262)
+++ src/main/org/apache/tools/ant/util/IdentityStack.java	(working copy)
@@ -17,6 +17,9 @@
  */
 package org.apache.tools.ant.util;
 
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
 import java.util.Stack;
 
 /**
@@ -101,5 +104,12 @@
         }
         return -1;
     }
+    
+    public synchronized boolean removeAll(Collection<?> c) {
+        if (!(c instanceof Set)) {
+            c = new HashSet(c);
+        }
+        return super.removeAll(c);
+    }
 
 }