Compile and run the following class:

---%<---
import java.io.StringReader;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.xml.sax.InputSource;
public class TestClone {
    public static void main(String[] args) throws Exception {
        String xml = "<root xmlns='urn:root'/>";
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(true);
        Document doc = factory.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));
        Element root = doc.getDocumentElement();
        assert root.getLocalName().equals("root");
        assert root.getNamespaceURI().equals("urn:root");
        Document dummy = factory.newDocumentBuilder().newDocument();
        Element clone = (Element) dummy.importNode(root, true);
        assert clone.getLocalName().equals("root");
        assert clone.getNamespaceURI().equals("urn:root");
        System.out.println("OK");
    }
}
---%<---

Until Mustang b46, this worked fine, but in b46 it throws an error:

---%<---
java version "1.4.2_08"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_08-b03)
Java HotSpot(TM) Client VM (build 1.4.2_08-b03, mixed mode)

OK
---%<---
java version "1.5.0_04"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_04-b05)
Java HotSpot(TM) Client VM (build 1.5.0_04-b05, mixed mode, sharing)

OK
---%<---
java version "1.6.0-ea"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.6.0-ea-b45)
Java HotSpot(TM) Client VM (build 1.6.0-ea-b45, mixed mode, sharing)

OK
---%<---
java version "1.6.0-ea"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.6.0-ea-b46)
Java HotSpot(TM) Client VM (build 1.6.0-ea-b46, mixed mode, sharing)

Exception in thread "main" org.w3c.dom.DOMException: NAMESPACE_ERR: An attempt is made to create or change an object in a way which is incorrect with regard to namespaces.
at com.sun.org.apache.xerces.internal.dom.AttrNSImpl.setName(AttrNSImpl.java:146)
at com.sun.org.apache.xerces.internal.dom.AttrNSImpl.<init>(AttrNSImpl.java:115)
at com.sun.org.apache.xerces.internal.dom.CoreDocumentImpl.createAttributeNS(CoreDocumentImpl.java:2109)
at com.sun.org.apache.xerces.internal.dom.CoreDocumentImpl.importNode(CoreDocumentImpl.java:1622)
at com.sun.org.apache.xerces.internal.dom.CoreDocumentImpl.importNode(CoreDocumentImpl.java:1586)
at com.sun.org.apache.xerces.internal.dom.CoreDocumentImpl.importNode(CoreDocumentImpl.java:1528)
at TestClone.main(TestClone.java:18)
---%<---