ngFor + ngModel: How can I unshift values to the array I am iterating?

I have an array of elements which the user can not only edit, but also add and delete complete array elements. This works nicely, unless I attempt to add a value to the beginning of the array (e.g. using unshift).

Here is a test demonstrating my problem:

import { Component } from '@angular/core';
import { ComponentFixture, TestBed } from '@angular/core/testing';
import { FormsModule } from '@angular/forms';


@Component({
    template: `
        <form>
            <div *ngFor="let item of values; let index = index">
                <input [name]="'elem' + index" [(ngModel)]="item.value">
            </div>
        </form>`
})
class TestComponent {
    values: {value: string}[] = [{value: 'a'}, {value: 'b'}];
}

fdescribe('ngFor/Model', () => {
    let component: TestComponent;
    let fixture: ComponentFixture<TestComponent>;
    let element: HTMLDivElement;

    beforeEach(async () => {
        TestBed.configureTestingModule({
            imports: [FormsModule],
            declarations: [TestComponent]
        });

        fixture = TestBed.createComponent(TestComponent);
        component = fixture.componentInstance;
        element = fixture.nativeElement;

        fixture.detectChanges();
        await fixture.whenStable();
    });

    function getAllValues() {
        return Array.from(element.querySelectorAll('input')).map(elem => elem.value);
    }

    it('should display all values', async () => {
        // evaluation
        expect(getAllValues()).toEqual(['a', 'b']);
    });

    it('should display all values after push', async () => {
        // execution
        component.values.push({value: 'c'});
        fixture.detectChanges();
        await fixture.whenStable();

        // evaluation
        expect(getAllValues()).toEqual(['a', 'b', 'c']);
    });

    it('should display all values after unshift', async () => {
        // execution
        component.values.unshift({value: 'z'});
        fixture.detectChanges();
        await fixture.whenStable();

        // evaluation
        console.log(JSON.stringify(getAllValues())); // Logs '["z","z","b"]'
        expect(getAllValues()).toEqual(['z', 'a', 'b']);
    });
});

The first two tests pass just fine. However the third test fails. In the third test I attempt to prepend "z" to my inputs, which is successful, however the second input also shows "z", which it should not.

(Note that hundreds of similar questions exist on the web, but in the other cases people were just not having unique name-attributes and they are also just appending, not prepending).

Why is this happening and what can I do about it?

from ngFor + ngModel: How can I unshift values to the array I am iterating?