Jasmine: Real function being called after spyOn with function reference

I have an angular service. Inside this service I have an object with a function, that references another function on the service. (Code below)

I want to use Jasmine (1.3) to spy on my service function, to verify that when the object's function gets called, it actually calls the real function.

My problem: After calling spyOn, the real function is still being called.

FooService.js

angular.module('foo').service("FooService", function() {
     var self = this;

     this.fooFunction = function() {
         console.log("Foo function is being called");
     }

     this.bar = {
         barFunction : self.fooFunction
     }
});

FooService-spec.js

describe("Testing FooService", function() {
     var service;

     beforeEach(inject(function(_FooService_) {
         service = _FooService_;
     }));

     describe("Test bar object", function() {
        it("should call fooFunction when bar.barFunction is called", function() {
             spyOn(service, "fooFunction");
             service.bar.barFunction();
             expect(service.fooFunction).toHaveBeenCalled();
         });
     });
 });

I have found that if I change FooServce.js to the following, this all works though:

FooService - Working

angular.module('foo').service("FooService", function() {
     var self = this;

     this.fooFunction = function() {
         console.log("Real function is being called");
     }

     this.bar = {
         barFunction : function() {
             return self.realFunction();
         }
     }
 });

What part of JavaScript / Angular / Jasmine am I failing to understand in the first example?