Why is a model one-time readable in an AngularJS controller?

I'm trying to read a model from inside a controller. Say I have this controller

angular.module('app', [])
  .controller('MainCtrl', function($scope) {
    $scope.data = {title: 'foo'};

    $scope.log = function() {
      console.log($scope.data);
    }
  });

And this markup

<div ng-app="app" ng-controller="MainCtrl">
  <input ng-model="data.title">
  <button ng-click="log()">log</button>  
</div>

When I press the button the first time it works, also if I modified the value, but all subsequent clicks just logs the first model again, no matter if the input data is changed.

What am I not getting? Should I use something else for this purpose? A service?

Fiddle: http://jsfiddle.net/J6jLz/1/

Update Curiously it works if I log the 'title' property prior to logging the actual data object: http://jsfiddle.net/Yf5kz/4/

Does this have to do with $apply on the scope maybe?