Model protected properties - Bug?

As this does not throw an error;

class Robots extends \Phalcon\Mvc\Model {
    protected $name;

    public function setName($name)
    {
        $this->name = $name;
    }
}

$robot = new Robots();
$robot->name = "Bumblebee";
$robot->save();

but the following does;

// Notice: Access to undefined property ...
echo $robot->name;

should I override the magic __set() function (in Robots) and throw an Exception, or is it a bug?