PortletRequest handling of attributes with reserved prefix ('java' or 'javax') is not consistent between getAttribute and getAttributeNames. Former returns values for reserved attributes while latter doesn't iterate over them. I can't find reference from spec which restricts reserved attributes from being iterated over.
This is annoying when framework on top of the api obscures request attribute semantics. Hence attributes like "javax.portlet.faces.defaultViewId" have to be used with extreme caution.