[datepicker] active state on every first day of the month

Don't know if that's the intended behavior anyway it seems weird to me that while navigating on and back through the months, day one is always marked as active (and couldn't find an option to disable this behavior). To see it open this page: http://plnkr.co/edit/F3cu3Fed6DhgjxJnxT0J?p=preview and click on the right arrow over and over...