title: Composer removing random files from package after installation
body: <p>this is the console output (shortened a bit):</p>
  
  <pre><code>λ composer require mpdf/mpdf
  Using version ^6.1 for mpdf/mpdf
  ./composer.json has been updated
  Loading composer repositories with package information
  Updating dependencies (including require-dev)
  Package operations: 2 installs, 0 updates, 0 removals
    - Installing setasign/fpdi (1.6.2): Downloading (100%)
    - Installing mpdf/mpdf (v6.1.3): Downloading (100%)
  Writing lock file
  Generating autoload files
  Removed 31 files or directories.
  </code></pre>
  
  <p>Why the hell is there the last line? When I then try to use mPDF in my project, it doesn't work (file not found), because most of the mPDF source files are really missing in the directory. When I lookup in the composer cache, all the files are there, so composer probably installs all the files and then randomly removes 31 files or directories. Why? And how can I fix this? I tried using a newer version of the package, same problem.</p>
  
  <p>Composer version: 1.5.2 (just updated)
  Also cache cleared just before the command.</p>