title: Deletion of nested attributes does not work
body: <p>I seem to be unable to delete items using the <code>accepts_nested_attributes_for</code> command but I have done this according to <a href="http://railscasts.com/episodes/196-nested-model-form-revised" rel="nofollow noreferrer">this tutorial</a> and the associated <a href="https://github.com/railscasts/196-nested-model-form-revised/tree/master/questionnaire-after" rel="nofollow noreferrer">git repo</a>. My models are ...</p>
  <pre><code>class Job &lt; ActiveRecord::Base
      has_many :specialties, :inverse_of =&gt; :job
      accepts_nested_attributes_for :specialties, allow_destroy: true, :reject_if =&gt; :all_blank
  end
  
  class Specialty &lt; ActiveRecord::Base
      belongs_to :job, :inverse_of =&gt; :specialties
  end
  </code></pre>
  <p>In my <code>Job</code> form, I have...</p>
  <pre><code>&lt;%= f.check_box :_destroy %&gt;
  &lt;%= f.label :_destroy, &quot;Remove Specialty&quot; %&gt;
  </code></pre>
  <p>When I click the checkbox to delete the a couple of <code>specialties</code>, nothing happens. I checked the server output and received:</p>
  <blockquote>
  <p>Started PATCH &quot;/jobs/1&quot; for 127.0.0.1 at 2013-07-16 16:15:16 -0400</p>
  <p>Processing by JobsController#update as HTML</p>
  <p>Parameters: {&quot;utf8&quot;=&gt;&quot;✓&quot;, &quot;authenticity_token&quot;=&gt;&quot;8VxYXujcKXpLEm8+7B43SLU6X3fH00kIOmFK+nvaBKs=&quot;, &quot;job&quot;=&gt;{&quot;name&quot;=&gt;&quot;Cook&quot;, &quot;description&quot;=&gt;&quot;Makes the food.&quot;, &quot;specialties_attributes&quot;=&gt;{&quot;2&quot;=&gt;{&quot;name&quot;=&gt;&quot;&quot;, &quot;description&quot;=&gt;&quot;&quot;, &quot;_destroy&quot;=&gt;&quot;1&quot;, &quot;id&quot;=&gt;&quot;3&quot;}, &quot;3&quot;=&gt;{&quot;name&quot;=&gt;&quot;&quot;, &quot;description&quot;=&gt;&quot;&quot;, &quot;_destroy&quot;=&gt;&quot;1&quot;, &quot;id&quot;=&gt;&quot;4&quot;}}}, &quot;commit&quot;=&gt;&quot;Update Job&quot;, &quot;id&quot;=&gt;&quot;1&quot;}</p>
  <p>Job Load (0.1ms)  SELECT &quot;jobs&quot;.* FROM &quot;jobs&quot; WHERE &quot;jobs&quot;.&quot;id&quot; = ? LIMIT 1  [[&quot;id&quot;, &quot;1&quot;]]</p>
  <p><strong>Unpermitted parameters: _destroy</strong></p>
  <p><strong>Unpermitted parameters: _destroy</strong></p>
  <p><strong>Unpermitted parameters: _destroy</strong></p>
  <p><strong>Unpermitted parameters: _destroy</strong></p>
  </blockquote>
  <p>What did I miss? I've gone through the tutorial and repo a bunch of times and I can't see where I've gone off.</p>