Nested checkbox in ngbTabTitle not working

I'm trying to put a checkbox in a tabset title, but it doens't seem to work. I really appreciate some help. My simplified code look like this:

    <ngb-tabset>
        <ngb-tab>
            <ng-template ngbTabTitle>
                <input type="checkbox" [(ngModel)]="selectedTabs" (click)="selectTab(i)" />
                Result
            </ng-template>

            <ng-template ngbTabContent>
                <input type="checkbox" [(ngModel)]="selectedTabs" (click)="selectTab()" />
                ...

The model is being changed as I can see in the second "test-checkbox" and the console, but the activation-state is not shown by the checkbox in the title. Does anybody has an idea how this can going to work, please?

regards, Lars