Custom headers seems not to be working

[nei]

Guys, I am trying to setup custom headers but it seems not to work. The way I am setting up the header is this
...
casper.start();
tests.forEach(function (test) {

    console.log('Running Phantom CSS on Url: ' + test.url);
    casper.open(test.url, {
        method: 'get',
        headers: {
            'Host': 'mydomain.com'
        }
    }).then(function(response) {

...