Not sure why you went to Ford but I'd expect them to deny all responsibility and suggest you contact the bumper guys.
In 2004 I (and others) was having a problem with a box brake. I installed a brake light on the towed dash that was visible in the rear view mirror. The problem was resolved but it took time. Current rig has a cab brake light that is activated by the toed brakes, but no issues since the fix and no longer have a box brake.
Keep us informed but I doubt Ford will fix it and certainly they won't replace it.