HTML encoded String not translating correctly in AngularJS

I have an HTML encoded string like this:

Sign up and get <span class="strong">Something for     FREE!</span>

When I use ngSanitize and ng-bind-html in my template like this:

<p ng-bind-html="someText"></p>

I get back the HTML decoded string:

Sign up and get <span class="strong">Something for Free!</span>

But it literally shows the HTML decoded string in browser, instead of rendering the HTML correctly.

How can I have it render the correct HTML in the DOM?

You can decode the html string first. Here's a working plunker example.

angular.module('app', ['ngSanitize'])
  .controller('ctrl', ['$scope', '$sanitize', function($scope, $sanitize){
    $scope.someText = htmlDecode("Sign up and get <span class="strong">Something for     FREE!</span>");

    function htmlDecode(input){ 
      var e = document.createElement('div');
      e.innerHTML = input;
      return e.childNodes.length === 0 ? "" : e.childNodes[0].nodeValue;
    }
}]);

** Decode function taken from this answer.