link-to works in index.hbs but not in application.hbs

When I do a from index.hbs, everything works fine. I transition to cars/category -> templates/cars/category.hbs.

However, when I do the same from application.hbs (for navigation), I transition to an empty page and then automatically transition to the parent route cars.index -> templates/cars/index.hbs.

There is probably some logic to this. How can I transition to this route from a link click in application.hbs?

(a hard link <a href="/cars/mini" works fine, but I'll lose the state of the application.)

---

routes/cars/category.js model:

model(params) {
    return this.store.findRecord('cars/category', params.category_id, {backgroundReload: false});
}

---

In route.js:

this.route('cars', () => {
    this.route('cars/category', { path: '/cars/:category_id' });
});