title: Laravel (5.3) pluck collection is returning other results than array
body: <p>I've encoutered something strange. I'm making a selectbox, and i'm using the pluck method on a database model.</p>
  
  <p>This piece of code:</p>
  
  <pre><code>    $orgs = Organisation::pluck('name', 'id');
      dd($orgs);
  </code></pre>
  
  <p>Gives me the following results:</p>
  
  <pre><code>Collection {#611 ▼
    #items: array:6961 [▼
      0 =&gt; "Test organisatie"
      1 =&gt; "Name"
      2 =&gt; "Another"
  </code></pre>
  
  <p>As you can see, the ID is not present. </p>
  
  <p>Now when i make it into an array:</p>
  
  <pre><code>    $orgs = Organisation::pluck('name', 'id')-&gt;toArray();
      dd($orgs);
  </code></pre>
  
  <p>It gives the following results:</p>
  
  <pre><code>array:6961 [▼
  1 =&gt; "Test organisatie"
  3 =&gt; "Name"
  19 =&gt; "Another"
  </code></pre>
  
  <p>The array is perfectly usable, i just don't understand why there's a difference. </p>
  
  <p>--Edit:
  When i use the collection in the select form helper, it does display the keys properly. Making me think it's a bug in the var dumper?</p>