Relative path on windows

Incorrect generator behaviour on Windows (it fails):

C:/ruby/lib/ruby/1.8/pathname.rb:709:in relative_path_from': different prefix:<br/> "C:/" and "D:/work/ruby/test" (ArgumentError)

    from C:/ruby/lib/ruby/gems/1.8/gems/radiant-0.8.1/vendor/rails/railties/lib/rails_generator/lookup.rb:110:in `use_component_sources!'
    from C:/ruby/lib/ruby/gems/1.8/gems/radiant-0.8.1/vendor/rails/railties/lib/rails_generator/lookup.rb:109:in `each'

...

System configuration:
Rails 2.3.5 + Ruby 1.8.6 + Win XP 32bit

Steps to reproduce:
1. Place ruby on a C: drive, place rails on a D: drive.
2. Use some generator tools.
3. Get the exception.

The root cause is in the lib/rails_generator/lookup.rb (line 110):
relative_path = Pathname.new(File.expand_path(path)).relative_path_from(Pathname.new(::RAILS_ROOT))

The relative_path_from raises an ArgumentError in the described case.
Workaround is to patch the lib/rails_generator/lookup.rb and catch the exception.
Dirty patch is to modify the 110 line in lib/rails_generator/lookup.rb:
begin
relative_path = Pathname.new(File.expand_path(path)).relative_path_from(Pathname.new(::RAILS_ROOT)) rescue ArgumentError
relative_path = Pathname.new(File.expand_path(path)) end