Hook methods not found in Typescript derived classes unless present on ancestor

Framework Knowledge
1

When the ancestor Scope does not define attached or detached methods, the hook methods attached and detached in the view-model below are not invoked.

import { Item } from '../item';
import { Scope } from '../scope/scope';

export class RepeatingSection extends Scope {
  public TemplateModel: any;
  private UpdateTimerHandle: number;
  public activate(activationParameter: any) {
    super.activate(activationParameter);
    this.TemplateModel = JSON.parse(`{"Type": "scope", "Children": ${this.Model.Template}}`);
  }
  public attached() {
    console.log("attached");
  }
  public detached() {
    console.log("detached");
  }
  public add(): void {
    // update the model and binding adds the item (which is a view-model)
    let raw = `{ "Type": "scope", "Children": ${this.Model.Template} }`;
    let row = JSON.parse(raw);
    this.Model.Children.push(row);
  }
  public remove(item: Item): void {
    // update the model, and binding removes the item (which is a view-model)
    this.Model.Children.splice(this.Model.Children.indexOf(item.Model), 1);
  }
}

Adding stub methods to Scope causes Aurelia to find the methods on RepeatingSection

  public attached(): void {
    //this exists because without it Aurelia can't find attached on RepeatingSection
  }
  public detached(): void {
    //this exists because without it Aurelia can't find attached on RepeatingSection
  }