Why doesn't the handlebars "if" helper call the actual model computed property?

I'm maintaining an application in Ember, and this "computed property" never actually gets computed by the if block helper in the template.

Model:

var item = App.Item.create({
    isAddedToCart: function () {
        console.log('addedToCart method has been called');
        return false;
    }.property()
});

Template:

In my component that is in the template, the console.log() never gets called, but the function seems to be tested if it's truth-y or not. Is there something wrong in my approach?