No clarity on data returned from my $httpBackend.whenPOST while writing testcases in Karma+Jasmine

While writing unit-tests, I found two different scenarios of $hhtpBackend

first case:

$httpBackend.when('POST', "/rest/path").respond({
                "errorCode":"OK"});

Here data received as

 Object{data: Object{errorCode: 'OK'}, status: 200, headers: function (c) { ... }....}

second case:

$httpBackend.when('POST', "/rest/anotherpath").respond({
                    "errorCode":"OK"});

Here data received as

{errorCode: 'OK'}

I don't know why I am getting two different responses in two different scenarios. Please some one help me to figure it out. Thanks in Adavnce.