this is a extended question (so not a duplicate) to this:
Angular2 Dynamic input field lose focus when input changes
I made the angular tutorial: https://angular.io/guide/dynamic-form#dynamic-forms
And copied the classes as they are in the plunker example.
The Angular Tut uses native arrays and it dont lose focus in the plunker example.
But my project lose focus onChange. What did I wrong in compare to angular? And why their example dont lose focus even if they use native array and no "TrackBy" work around?