title: Why is older version of sass-rails require higher version of railties (Bundler)
body: <p>I have in my Gemfile</p>
  
  <pre><code>gem 'rails', '4.0.0'
  gem 'sass-rails', '~&gt; 4.0.0'
  </code></pre>
  
  <p>This works fine. If I run bundle update it says "Using sass-rails (4.0.1)". Now if I try to change it to use 4.0.0 (<code>gem 'sass-rails', '4.0.0'</code>) and run bundle update, it gives me error:</p>
  
  <pre><code>Bundler could not find compatible versions for gem "railties":
    In Gemfile:
      rails (= 4.0.0) ruby depends on
        railties (= 4.0.0) ruby
  
      sass-rails (= 4.0.0) ruby depends on
        railties (4.0.1)
  </code></pre>
  
  <p>I don't understand why lower version sass-rails requires higher version railties? That seems strange to me, how can that be? In fact that's a lie!</p>
  
  <p>In another project (Rails Tutorial sample_app) I have</p>
  
  <pre><code>gem 'rails', '4.0.0'
  gem 'sass-rails', '4.0.0'
  </code></pre>
  
  <p>and only railties (4.0.0), yet bundle update works fine. So it seems the error above is not the problem. Then I don't know what is?!</p>
  
  <p>I found more info here - <a href="https://stackoverflow.com/questions/19439302/cant-get-gemfile-to-allow-for-bundle-update">can&#39;t get gemfile to allow for bundle update</a> (if I switch order of rails and sass-rails in gemfile then 4.0.0 works fine).
  However it still doesn't make sense why my Gemfile works fine in one project and not the other with the same sass-rails and rails gems and the same railties.</p>