title: Why changing heroku buildpack for existing app doesn't run bin/release
body: <p>I had a php app on heroku with the default buildpack (apache), and then decided to change it to the php-fpm + nginx buildpack (<a href="https://github.com/iphoting/heroku-buildpack-php-tyler/" rel="nofollow">https://github.com/iphoting/heroku-buildpack-php-tyler/</a>).</p>
  
  <p>I issued the change command:</p>
  
  <pre><code>heroku config:set BUILDPACK_URL=https://github.com/iphoting/heroku-buildpack-php-tyler.git
  </code></pre>
  
  <p>And pushed with:</p>
  
  <pre><code>git push heroku master
  </code></pre>
  
  <p>The slug then compiles, but all the binaries fail to execute with "command not found", because PATH config variable which should be updated with bin/release isn't updated.</p>
  
  <p>In comparison, when creating an app from scratch with this buildpack with</p>
  
  <pre><code>heroku create -b https://github.com/iphoting/heroku-buildpack-php-tyler.git
  </code></pre>
  
  <p>Everything runs as expected (and PATH is present and updated).</p>
  
  <p>My assumption is that bin/release was not run after changing the config variable BUILDPACK_URL, and therefore the PATH variable isn't set.</p>
  
  <p>In order to make the app work, I had to manually add the PATH config variable. Did anybody else ever encounter this? Is this the expected behavior? By my understanding, bin/release should always run after a slug compile? </p>
  
  <p>EDIT: corrected the git url to the correct ".git" one</p>