what's the correct behavior of directory-namestring

Hi there,

I am using SBCL on Windows. I also have SBCL install on Debian Linux and 
FreeBSD.

I have to deal with some pathnames, for example:
#P"R:/Temp/abc/"

When passing the pathname to directory-namestring in SBCL 2.5.7 on 
Windows, I got:

* (directory-namestring #P"R:/Temp/abc/")
"/Temp/abc/"

SBCL 2.2.9 on Debian and 2.5.6 on FreeBSD, booth give:

* (directory-namestring #P"R:/Temp/abc/")
"R:/Temp/abc/"

Which is the correct behavior?

Best,
Jinsong