strange pathname?

* (make-pathname :name "cgi-bin/")
#P"cgi-bin/"
* (merge-pathnames "nav.py" #P"cgi-bin/")
#P"cgi-bin/nav.py"    ; **it is ok**
* (merge-pathnames "nav.py" (make-pathname :name "cgi-bin/"))
#P"nav.py"            ; why ?

*(defvar bp #P"/media/E/myapp/cgi-bin/")
* bp
#P"/media/E/myapp/cgi-bin/")
* (merge-pathnames "nav.py" bp)
#P"nav.py"            ; why ?
* (merge-pathnames "nav.py" #P"/media/E/myapp/cgi-bin/")
#P"/media/E/myapp/cgi-bin/nav.py"    ; **it is ok**

Я использую sbcl-1.0.54.

Любое предложение будет оценено по достоинству!