ConcurrentModificationException in CachedClass when running same script in multiple threads

java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
        at java.util.HashMap$KeyIterator.next(HashMap.java:828)
        at java.util.AbstractCollection.addAll(AbstractCollection.java:305)
        at org.codehaus.groovy.reflection.CachedClass.getInterfaces(CachedClass.java:70)
        at org.codehaus.groovy.reflection.CachedClass.initialize(CachedClass.java:134)
        at org.codehaus.groovy.reflection.ReflectionCache.getCachedClass(ReflectionCache.java:276)
        at org.codehaus.groovy.runtime.metaclass.MetaClassRegistryImpl.getGlobalMetaClass(MetaClassRegistryImpl.java:250)
        at org.codehaus.groovy.runtime.metaclass.MetaClassRegistryImpl.access$100(MetaClassRegistryImpl.java:45)
        at org.codehaus.groovy.runtime.metaclass.MetaClassRegistryImpl$LocallyKnownClasses.getFromGlobal(MetaClassRegistryImpl.java:112)
        at org.codehaus.groovy.runtime.metaclass.MetaClassRegistryImpl$LocallyKnownClasses.getMetaClass(MetaClassRegistryImpl.java:88)
        at org.codehaus.groovy.runtime.metaclass.MetaClassRegistryImpl$MyThreadLocal.getMetaClass(MetaClassRegistryImpl.java:361)
        at org.codehaus.groovy.runtime.metaclass.MetaClassRegistryImpl.getMetaClass(MetaClassRegistryImpl.java:265)
        at org.codehaus.groovy.runtime.InvokerHelper.getProperty(InvokerHelper.java:178)
        at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.getProperty(ScriptBytecodeAdapter.java:477)

    private Set interfaces;

    public Set getInterfaces() {
        if (interfaces == null)  {
            interfaces = new HashSet (0);

            if (getCachedClass().isInterface())
              interfaces.add(this);

            Class[] classes = getCachedClass().getInterfaces();
            for (int i = 0; i < classes.length; i++) {
                final CachedClass aClass = ReflectionCache.getCachedClass(classes[i]);
                if (!interfaces.contains(aClass))
                  interfaces.addAll(aClass.getInterfaces());
            }

            final CachedClass superClass = getCachedSuperClass();
            if (superClass != null)
              interfaces.addAll(superClass.getInterfaces());
        }
        return interfaces;
    }

            CachedClass fasterCachedClass = null;

            // Double-check put.
            synchronized (CACHED_CLASS_MAP) {
                ref = (SoftReference) CACHED_CLASS_MAP.get(klazz);

                if (ref == null || (fasterCachedClass = (CachedClass) ref.get()) == null) {
                    CACHED_CLASS_MAP.put(klazz, new SoftReference(cachedClass));
                } else {
                    // We must use the one that there first, we should be able to safely toss the one we made.
                    // By locking Class we would eliminate this race, but until the design is corrected we risk
                    // deadlock.
                    cachedClass = fasterCachedClass;
                }
            }

            if (null == fasterCachedClass) {
                // We've got a new CacheClass, now get loaded into the assignableMap.
            	cachedClass.initialize();
            }