guard failing silently on Windows

I'm trying to get guard to run guard-sass and guard-jammit on Windows 7 x64, and the behaviour I'm seeing is that it runs, pauses then exits silently, even with --debug active.

We are trying to get our designers (who work on windows, for better or worse), to build things using HAML/SASS and to use automated magnification/asset bundling with Jammit, as opposed to hand-assembling this stuff.

Here is a typical run:

C:\Users\Shibbles\Documents\Inspire>bundle exec guard start --debug

C:\Users\Shibbles\Documents\Inspire>

My Gemfile looks like this:

source 开发者_如何学编程'http://rubygems.org'

gem 'rack', '1.2.1'

gem 'linecache' # 1.8.7

gem 'rails', '3.0.9'
gem 'mysql2', '0.2.7'
gem 'capistrano'
gem 'capistrano-ext'
gem 'awesome_print'
gem "will_paginate", "~> 3.0.pre2"
gem 'haml'
gem 'haml-rails'
gem 'sass'
gem 'factory_girl'
gem 'factory_girl_rails'
gem 'jquery-rails', '>= 1.0.3'
gem 'devise'
gem 'guard'
gem "acts_as_list", "~> 0.1.3"
gem 'jammit'
gem 'win32-open3', :platforms => [:mingw_18, :mingw, :mswin]
gem 'rb-fchange', :platforms => [:mingw_18, :mingw, :mswin]
gem 'rb-notifu', :platforms => [:mingw_18, :mingw, :mswin]

group :development, :test do
  gem 'ruby-debug' # 1.8.7
  gem "rspec"
  gem 'rspec-rails'
  gem 'cucumber'
  gem 'cucumber-rails'
  gem 'capybara'
  gem 'database_cleaner'
  gem 'spork', '~> 0.9.0.rc'
  gem 'rcov'
  gem "guard-sass"
  gem 'guard-rspec'
  gem 'guard-spork'
  gem 'guard-bundler'
  gem 'guard-delayed'
  gem 'growl'
  gem 'webrat'
  gem 'guard-shell'
end