problem of uripath.refTo

I used cwm in python and wanted to generate RDF without the base URL
appearing in the final output. However, even if I provide the base URL
in the output mehtods rdfString() and n3String(), sometimes it doesn't
work perfectly.

The problem may be due to the behaviour of the uripath.refTo method.
For example:

uripath.refTo('http://www.example.com/test', 'http://www.example.com/test#foo')

returns

'/test#foo'