Default input datepicker validation blocked

[AlexFreem]

I am apply little moddifications to default codepen of Angular Material Datepicker:

http://codepen.io/anon/pen/qOxNMr

Now we can see form model. By default, default datepicker goes with "$invalid : true" value. But on screen we didnt see any problems with datepicker.

If we manualy change current date ( on last datepicker ) to something what contains string, for example, - datepicker goes invalid and red line will shown. $invalid is still true.

Now change to normal date. Datepicker state goes normal, but $invalid is still true.