Actions sent from child route aftermodel hook aren't catched in parent route

Let me show you my configuration before explaning my problem. So here is an extract of my router :

Router.map(function() {
    [...]
    this.route('parent', {path: '/:parent_slug'}, function () {
        this.route('child', {path: '/:child_slug'});
    });
});

The parent route displays a component which need the parent_slug and optionally the child_slug. So in the child route afterModel() hook, I send an action to the parent route to update the child_slug it gives to the component.

In the child route :

afterModel(model) {
    [...]
    this.send('myAction', model.childSlug);
    [...]
}

In the parent route :

actions: {
    myAction(slug) {
        this.set('childSlug', slug);
    }
}

If I load the parent route first and then do a transition to the child route, the action will be sent and correctly catched by the parent but if I load the child route directly, the action is not catched. I tried to catch the action in the application route and it works.

So I guess that during the afterModel() hook of the childroute, the parents route actions aren't loaded yet.

Do you guys know if it's a bug or it's a normal behaviour ? I mean to start loading the child route before the parent one is completely loaded ?

Thank you !