For me, this solves the bug.
It is against version 2007-06-26
When putting debug info in inc/parser/xhtml.php, I get this on screen:
wiki:/wiki/test/page
That is, the current namespace is added because the code searches a ':' and there is only '/' as directory separators.
Some more tests can be added in order to use $conf['sepchar'] too
HTH
Oliver