Ember transition doesn't work after destroyRecord

I am very new to ember, but I've spent hours with this problem and can't solve it on my own. Here's my route (using ember-cli):

import Ember from 'ember';

export default Ember.Route.extend({
    actions: {
        save: function() {
            var controller = this.controller;
            controller.get('model').save().then(function(account) {
                console.log('account saved');
                controller.transitionToRoute('accounts.index');
            }, function(response) {
                console.log('account NOT saved');
            });

            return false;
        },
        deleteAccount: function() {
            var controller = this.controller;
            controller.get('model').destroyRecord().then(function(account) {
                console.log('account deleted');
                controller.transitionToRoute('accounts.index');
            }, function(response) {
                console.log('account NOT deleted');
            });

            return false;
        },
        cancel: function() {
            this.controller.get('model').rollback();
            this.transitionToRoute('accounts.index');
            return false;
        },
    }
});

I am triggering the deleteAccount action in my template (button). The interesting thing is that the code is actually deleting the record. It sends a successful delete request and the api deletes the account. But it never transitions to accounts.index. Instead it logs "account NOT deleted". If I manually go to account.index then the model isn't there any more (as one would expect). I got the code from the official ember docs. See: http://ift.tt/1FjIryj

So why is the promise always failing when the model is actually deleted? Your help would be very much appreciated!

Btw.: It is an edit route with account_id passed as param, so no need for manually defining a "model function" on the route. Just in case someone was wondering.