XPath problem with namespace attribute

All,

I hope it is ok to post this XPath comment to this list.

It seems there is a bug in the XPath result when an empty namespace
attribute is used:

XML:
<?xml version="1.0" encoding="utf-8"?>
<One>
  <Two>
    <Three xmlns="http://www.hailstone.org/">
      <Four>
          <Five/>
      </Four>
    </Three>
  </Two>
</One>

XPath:
/One/Two/Three/Four/Five

Expected Result:
The element "Five" should be returned.

Result:
Nothing is returned.

Modifications of element "Three" that fix the problem:

...
<Three xmlns:something="http://www.hailstone.org">
...

...
<Three normalattribute="http://www.hailstone.org">
...

Is this a bug in the XPath implementation?
Is there something something special about the "xmlns" attribute that
I don't know?

Thoughts?

Thanks,
Matthew