Why does the filter not work immediately?

Question

Angular

Added a datepicker, hung a change of variables in the scope on the change event. When dates change, this event occurs (can be seen in the console). But for some reason, the filter event occurs only after a click outside the datepicker, and even then not always (you can also look in the console).
Here is the code: https://jsfiddle.net/t3jzedta/3/
Why is that?
ps datepicker with interval selection

Answer 1

Google how change tracking works in Angular (Angular digest cycle).