[plt-scheme] URLs with passwords

The delicious API (http://delicious.com/help/api) requires URLs like the 
following:

    https://user:password@api.del.icio.us/v1/posts/get?tag=foo

But I can't seem to construct such a URL with the net/url library.  The 
colon between user and password always gets encoded. So for example,

(url->string
  (string->url
    "https://user:password@api.del.icio.us/v1/posts/get?tag=foo"))

==>

"https://user%3Apassword@api.del.icio.us/v1/posts/get?tag=foo"

Is this a bug, or is there some other way to construct the appropriate 
URL?  (This is in 4.1.3.3-svn3dec2008).

David