title: wp_title filter takes no effect on the <title> tag
body: <p>I just added the following filter in my theme <code>functions.php</code> file:</p>
  
  <pre><code>function change_the_title() {
      return 'My modified title';
  }
  add_filter('wp_title', 'change_the_title');
  </code></pre>
  
  <p>And in my <code>header.php</code>:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html &lt;?php language_attributes(); ?&gt;&gt;
  &lt;head&gt;
      &lt;meta charset="&lt;?php bloginfo( 'charset' ); ?&gt;"&gt;
      &lt;meta id="viewport" name="viewport" content="width=device-width"&gt;
      &lt;link rel="profile" href="http://gmpg.org/xfn/11"&gt;
      &lt;link rel="pingback" href="&lt;?php bloginfo( 'pingback_url' ); ?&gt;"&gt;
      &lt;?php wp_head(); ?&gt;
  &lt;/head&gt;
  &lt;body &lt;?php body_class();?&gt;&gt;
  </code></pre>
  
  <p>Then, I found the title of my page did <strong>NOT</strong> change! And the title tag was injected in the <code>wp_head</code> function.</p>
  
  <p>More, if I call the function <code>wp_title</code> manually in the header, it does return the expected value.</p>
  
  <p>What's the matter? How can I work around it?</p>
  
  <hr>
  
  <p>Addition: My WordPress version is 4.4.</p>