The <b>
appears as data not a tag. It will either be represented as <b>
or appear in a CDATA block.
i.e. the XML contains a fragment of HTML as data. It doesn't include namespaced XHTML.
The output is what you should expect.
What do you next depends on what you want to achieve. Whatever it is, you need to get the data as a string (rather then a textNode) and treat that string as HTML, not text.
If you want to query the HTML, then you need to run it through an HTML parser first.