title: Composer dump-autoload doesn't work successfully
body: <p>Composer dump-autoload doesn't work successfully unless the optimize flag (-o) is used.</p>
  
  <p>I have a composer.json with the following: </p>
  
  <pre><code>  "autoload": {
  "psr-4": {
    "ClassSrcFolder_TopLevelNamespace\\": "app/ClassSrcFolder/"
  }
  </code></pre>
  
  <p>}</p>
  
  <p>Running "composer dump-autoload" w/o the -o flag I get a "class not found" error for a sub-folder to the "app/ClassSrcFolder/"</p>
  
  <p>Is there a reason for this behavior?</p>