XmlNodePointer does not handle namespace prefixes with repeated URNs

There are still problems with the XML Namespace handling of XmlNodePrinter in 1.6 Beta 2. The following code parses valid XML and then writes it out to a string. The string no longer contains valid XML because one of the namespace prefixes has been lost.

def x="<Foo xmlns='urn:a' xmlns:f='urn:a'><f:Bar xmlns='urn:b'><haha/></f:Bar></Foo>"
def y = new XmlParser(false, true).parseText(x)
def writer = new StringWriter()
def xnp = new XmlNodePrinter(new PrintWriter(writer))
xnp.namespaceAware = true
xnp.print(y)
print writer.toString()

Output is (note missing declaration for namespace prefix f

<Foo xmlns="urn:a">
  <f:Bar>
    <haha xmlns="urn:b"/>
  </f:Bar>
</Foo>