Using save() is causing both POST and PUT

Hello folks,

When I perform a .save() I am noticing that my WebAPI is getting hit by a POST followed by a PUT.

cr.save().then(function (data) {
                cr.set('error', '');
            }, function (data) {
                cr.set("error", "Error: " + data.message);
            });

Any ideas what might be causing this?

Please advise.

Thanks.