I've noticed that request headers and cookies sent have disappear from network inspection in some cases (XHR request for example), at least with OSX Google Chrome.
If you don't see what I mean, just open the web inspector and connect to your Twitter account, then check the XHR requests: you can see request payload and response headers but headers and cookies sent have disappear.
Any idea how to fix this ? I've tried activating some exotic flags in about:flags but saw no changes.