Rake doesn't work with latest Compass? "uninitialized constant Sass::Script (NameError)"

Question

I've been playing with Octopress for few days and today wanted to try latest Susy v. 2.1.2 which requires Compass v. 1.0 (1.0.0.alpha.19 atm) which requires Sass v. 3.3 , as far as I know… Beside that, according to the Susy changelog, Susy is registered with Compass 1.0 automatically.

So I modified my Gemfile:

source "https://rubygems.org"

group :development do
  gem 'rake', '~> 10.0'
  gem 'jekyll', '~> 0.12'
  gem 'rdiscount', '~> 2.0.7'
  gem 'pygments.rb', '~> 0.3.4'
  gem 'RedCloth', '~> 4.2.9'
  gem 'haml', '~> 3.1.7'
  gem 'compass', '1.0.0.alpha.19'
  gem 'sass', '~> 3.3'
  gem 'sass-globbing', '~> 1.0.0'
  gem 'rubypants', '~> 0.2.0'
  gem 'rb-fsevent', '~> 0.9'
  gem 'stringex', '~> 1.4.0'
  gem 'liquid', '~> 2.3.0'
  gem 'directory_watcher', '1.4.1'
end

gem 'sinatra', '~> 1.4.2'

So I did bundle install. But it seems rake generate neither rake preview don't like new Compass at all. Gettin plenty of these:

/Library/Ruby/Gems/2.0.0/gems/compass-core-
    1.0.0.alpha.19/lib/compass/core/sass_extensions.rb:2:in `<top 
    (required)>': uninitialized constant Sass::Script (NameError)

Compass alone working without any problem. Though, I'm pretty new to Rake, Compass, Octopress so am I missing something?