Ember promise service function

For a couple of hours I have been trying to figure out how to have a promise in a service in Ember. I really can not understand why it seems to be impossible to not have a service function called if an earlier promise in the chain rejects.

To be more clear, I want to chain several promises which will be located in several different places (services). The simplified, working code, looks as follows:

return new Ember.RSVP.Promise(function(resolve, reject) {
    resolve();
}).then(function() {
    return new Ember.RSVP.Promise(function (resolve, reject) {
    Ember.run.later(function() {
        console.log('One');
        resolve();
    }, 3000);
});
}).then(function () {
    return new Ember.RSVP.Promise(function (resolve, reject) {
    Ember.run.later(function() {
        console.log('Two');
        resolve();
    }, 3000);
});
}).then(function () {
    return new Ember.RSVP.Promise(function (resolve, reject) {
    Ember.run.later(function() {
        console.log('Three');
        resolve();
    }, 3000);
});
}).then((resolve) => {
    console.log(resolve);
}, (reject) => {
    console.log(reject);
});

But when I try to replace the second promise function with a call to a service function containing the exact same promise, it starts to act weird.

return new Ember.RSVP.Promise(function(resolve, reject) {
    resolve();
}).then(this.get('demoService.serviceFunction')()).then(function () {
    return new Ember.RSVP.Promise(function (resolve, reject) {
        Ember.run.later(function() {
            console.log('Two');
            resolve();
        }, 3000);
    });
}).then(function () {
    return new Ember.RSVP.Promise(function (resolve, reject) {
        Ember.run.later(function() {
            console.log('Three');
            resolve();
        }, 3000);
    });
}).then((resolve) => {
    console.log(resolve);
}, (reject) => {
    console.log(reject);
});

In the second case, the demoService.serviceFunction is called regardless of whether the first promise is resolved or rejected. It does not matter if the function is called like this.get('demoService.serviceFunction')() or his.get('demoService').serviceFunction().

I have created a twiddle to demonstrate the problem: http://ift.tt/29DFVdO - The console always seems to be outputting ServiceFunctionCalled, where that should not be the case if the first promise is rejected.

Hopefully somebody can provide me insights on what I am doing wrong here. Thanks in advance!