xmlns in xpath query

Using postgresql v8.3 and xml xpath query function and having trouble with xmlns. Note: the select statements were originally all on a single line.

The xpath function works ok if the xmlns attributes are missing.

select xpath('/gpx', '<gpx  version="1.0" creator="GPSBabel - http://www.gpsbabel.org">abc</gpx>');

                                       xpath
-----------------------------------------------------------------------------------
 {"<gpx version=\"1.0\" creator=\"GPSBabel - http://www.gpsbabel.org\">abc</gpx>"}
(1 row)

The xpath function gives no result when xmlns attributes are supplied.

select xpath('/gpx', '<gpx xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.topografix.com/GPX/1/0" version="1.0" creator="GPSBabel - http://www.gpsbabel.org"  xsi:schemaLocation="http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd">abc</gpx>');

 xpath
-------
 {}
(1 row)

Setting the optional name space attributes for the xpath function also gives no results.

select xpath('/gpx', '<gpx xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.topografix.com/GPX/1/0" version="1.0" creator="GPSBabel - http://www.gpsbabel.org"  xsi:schemaLocation="http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd">abc</gpx>', array[array['xsi','http://www.w3.org/2001/XMLSchema-instance'],array['','http://www.topografix.com/GPX/1/0']]);

 xpath
-------
 {}
(1 row)


Suggestions?

-Frank