title: click event auto triggered on knockoutjs
body: <p>I'm trying on <a href="http://learn.knockoutjs.com/#/?tutorial=webmail">mail client tutorial</a> on learn.knockoutjs.com. I want to add a "back button" in mail detail block. But that button is auto triggered. </p>
  
  <p>my codes</p>
  
  <pre><code>&lt;div class="viewMail" data-bind="with: chosenMailData"&gt;
      &lt;button data-bind="click: alert('derp')"&gt;derp&lt;/button&gt;
      &lt;div class="mailInfo"&gt;
          &lt;h1 data-bind="text: subject"&gt;&lt;/h1&gt;
          &lt;p&gt;&lt;label&gt;From&lt;/label&gt;: &lt;span data-bind="text: from"&gt;&lt;/span&gt;&lt;/p&gt;
          &lt;p&gt;&lt;label&gt;To&lt;/label&gt;: &lt;span data-bind="text: to"&gt;&lt;/span&gt;&lt;/p&gt;
          &lt;p&gt;&lt;label&gt;Date&lt;/label&gt;: &lt;span data-bind="text: date"&gt;&lt;/span&gt;&lt;/p&gt;
      &lt;/div&gt;
      &lt;p class="message" data-bind="html: messageContent" /&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>when i set <strong>chosenMailData</strong> viewMail div is show. But same time browser alert "derp". I want to when i click button, browser alert at that time. what is wrong?</p>