If I pass the :lisp value to the NAMESTRING, ENSURE-PATHNAME *does* call PARSE-NAMESTRING.
Yes, looking at the spec for PARSE-NAMESTRING, this is a bug:
"If host is nil and thing is a syntactically valid logical pathname namestring containing an explicit host, then it is parsed as a logical pathname namestring."
So this is a clisp fail, 2.49 on Mac OS X (from Mac Ports).
If it works for you, perhaps this has already been fixed. I don't have time to build and run clisp from the repo.
I confirm that the bug is present in the CLISP package provided by Ubuntu 12.04.4 LTS, and not present in the CLISP binary I compiled from the most recent hg. So it must be a relatively recent bug fix.
—♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org Failure is not an option. It comes bundled with your Microsoft product. — Ferenc Mantfeld