Ruby Forum Ruby-core > pathname--is this a bug?

I'm thinking this is a bug...
thoughts?

>> Pathname.new('c:/').relative_path_from Pathname.new('/')
ArgumentError: different prefix: "c:/" and "/"
        from C:/installs/ruby191p243p2/lib/ruby/1.9.1/pathname.rb:742:in
`relative_path_from'
        from (irb):4
        from C:/installs/ruby191p243p2/bin/irb:12:in `<main>'