title: deep copy does not work, shallow copy works fine
body: <p>Would anyone know why the deep copy does not work in my case, the shallow copy/assignment works just fine:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>        vm.category = null;
  
          $http.get("/api/category/" + vm.categoryId)
              .then(function (response) {
                  //does not work
                  angular.copy(response.data, vm.category);
                  //works just fine
                  vm.category = response.data;
              }, function (error) {
                  vm.errorMsg = "There was an error retrieving category data: " + error;
              });</code></pre>
  </div>
  </div>
  </p>
  
  <p>This method for deep copy works fine:</p>
  
  <pre><code>vm.category = angular.copy(response.data);
  </code></pre>
  
  <p>why:</p>
  
  <pre><code>angular.copy(response.data, vm.category);
  </code></pre>
  
  <p>does not work?</p>