title: ngAnimate working on ng-leave but not ng-enter
body: <p>Consider the following CSS:</p>
  
  <pre><code>nav {
    position: fixed;
    z-index: 1900;
    top:0; right:0; bottom:0;
    width: 60px;
    -webkit-transition: right 600ms cubic-bezier(.3,1,.5,1);
    -moz-transition: right 600ms cubic-bezier(.3,1,.5,1);
    -o-transition: right 600ms cubic-bezier(.3,1,.5,1);
    transition: right 600ms cubic-bezier(.3,1,.5,1); }
  
  nav.ng-enter { right: -60px; }
  nav.ng-enter.ng-enter-active { right: 0; }
  
  nav.ng-leave { right: 0; }
  nav.ng-leave.ng-leave-active { right: -60px; }
  </code></pre>
  
  <p>Then of course I have ng-if attribute on the nav in the HTML:</p>
  
  <pre><code>&lt;nav ng-if="account.isLoggedIn &amp;&amp; navIsOpen"&gt;
    ...
  &lt;/nav&gt;
  </code></pre>
  
  <p>The animation works fine on ng-leave. I can also see in developer tools that the ng-enter and ng-enter-active classes are added for the correct transition duration, but instead of the transition happening, the element just appears in place. Why is this happening?</p>