header Content-Type case sensitivity issue in testing with superagent and jasmine-ajax

Question

I'm using superagent and jasmine-ajax in my testing environment (karma with jasmine adapter).

I noticed an issue pertaining to case-sensitivity on the response headers when trying to mock responses that superagent will then handle.

Testing code:

it('should parse the response as json', function() {
    var response = '{ "foo" : "bar" }';

    superagent.get('/some/url', function(
        expect(response.body).toEqual({ foo: "bar" });
    });

    jasmine.Ajax.requests.mostRecent().response({
        status: 200,
        // uncomment following line to make this test pass
        // responseHeaders: { "content-type" : "application/json" },
        responseText: response
    });

});

In superagent.js line ~695 has:

this.header['content-type'] = this.xhr.getResponseHeader('content-type');

In mock-ajax.js line ~175 has

this.responseHeaders = response.responseHeaders || 
    {"Content-type": response.contentType || "application/json" };

So, obviously within each respective library, there is a discrepancy with casing, but, according to spec, all the research I've done says that this field is case-insensitive. I thought that it might be an issue with PhantomJS, but I just tried using Chrome as well, but the same issue is present.

Any insight would be appreciated.