ADDITIONAL SYSTEM INFORMATION :
JDK 9.0.4 - works
JDK 10.0 onwards (including 18) - cloneMap returns empty list

A DESCRIPTION OF THE PROBLEM :
I was upgrading from Java 8 (works fine) to 11 calculating a digest value on an XML snippet. I was getting different result. Document.normalizeDocument returns different results when crossing over fro 9.0.4 to 10.0 onwards.

To pin point the bug. observer the call: 
DOMNormalizer.namespaceFixUp()
  Line 888: attributes.cloneMap(fAttributeList);

cloneMap does NOT work. NOTE this does not use the return value and replies on fAttributeList being passed by reference.

The implementation of clone map NamedNodeMapImpl.cloneMap():578 has changed. 
Line 580: list = new ArrayList<>(nodes);
This news the method parameter which leaves the reference passed in by DOMNormalizer empty. This worked fine on JDK 9.0.4.

Really the code should be:
fAttributeList = attributes.cloneMap(fAttributeList);
OR the implementation change back

REGRESSION : Last worked in version 8u331

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the source code provider under JDK 9.0.4 and a more recent JDK 10+. Different namespace attribute ordering because NamedNodeMapImpl.cloneMap is not working as intended.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I expected consistent results and the fAttributeList to be populated from cloneMap.
ACTUAL -
cloneMap is not populating variable fAttributeList 

---------- BEGIN SOURCE ----------
package test;

import java.io.StringWriter;
import org.w3c.dom.Attr;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.bootstrap.DOMImplementationRegistry;
import org.w3c.dom.ls.DOMImplementationLS;
import org.w3c.dom.ls.LSInput;
import org.w3c.dom.ls.LSOutput;
import org.w3c.dom.ls.LSParser;
import org.w3c.dom.ls.LSSerializer;

public class main {

  public static void main(final String[] args) {
    try
    {

      final DOMImplementationRegistry registry = DOMImplementationRegistry.newInstance();

      final DOMImplementationLS impl = (DOMImplementationLS) registry.getDOMImplementation("LS");

      final LSParser builder = impl.createLSParser(DOMImplementationLS.MODE_SYNCHRONOUS, null);

      final LSInput input = impl.createLSInput();
      input.setStringData("<xml/>");

      final Document document = builder.parse(input);
      final Element root = document.getDocumentElement();

      // Generate a single element
      final Element element = document.createElement("token");

      final Attr attr = element.getOwnerDocument().createAttributeNS("http://blah.xsd", "wsu");
      attr.setValue("Id");
      element.setAttributeNodeNS(attr);

      final Attr attr2 = element.getOwnerDocument().createAttributeNS("http://blah2.xsd", "wsu2");
      element.setAttributeNodeNS(attr2);

      final Attr attr3 = element.getOwnerDocument().createAttribute("aa");
      element.setAttributeNodeNS(attr3);

      final Attr attr4 = element.getOwnerDocument().createAttribute("zz");
      element.setAttributeNodeNS(attr4);

      final Attr attr5 = element.getOwnerDocument().createAttribute("tt");
      element.setAttributeNodeNS(attr5);

      root.appendChild(element);

      for ( int i = 0; i < element.getAttributes().getLength(); i++ )
      {
        System.out.println(element.getAttributes().item(i).getNodeName());
      }

      //final String originalXML = prettyPrintFromDocument(document);
      System.out.println("PRE normalise " + prettyPrintFromDocument(document));
      document.normalizeDocument();
      System.out.println("POST normalise " + prettyPrintFromDocument(document));

      for ( int i = 0; i < element.getAttributes().getLength(); i++ )
      {
        System.out.println(element.getAttributes().item(i).getNodeName());
      }
    }
    catch ( final Exception ex )
    {
      ex.printStackTrace();
    }
}

/**
 * Pretty prints a DOM document to a String.
 *
 * @param message the DOM document to serialise.
 * @return a string representation of the DOM message parameter.
 */
private static String prettyPrintFromDocument(final Document message) {
  try {
    final DOMImplementationRegistry registry = DOMImplementationRegistry.newInstance();

    final DOMImplementationLS impl = (DOMImplementationLS) registry.getDOMImplementation("LS");

    final LSSerializer writer = impl.createLSSerializer();
    final LSOutput output = impl.createLSOutput();

    final StringWriter sw = new StringWriter();

    output.setEncoding("UTF-8");
    output.setCharacterStream(sw);

    try {
      writer.getDomConfig().setParameter("format-pretty-print", Boolean.TRUE);
    } catch (final Exception ignore) {
    }

    writer.write(message, output);

    return sw.toString();
  } catch (final RuntimeException e) {
    throw e;
  } catch (final Exception e) {
    throw new RuntimeException(e);
  }
}
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
None at the moment.

Happy to provide more info. Using Eclipse as debugger.

FREQUENCY : always