the way to fix is this to reprogram the car which you do not want to use the remote for.
Example -- you want new remote for the focus, leave it as is.
now, follow reprogramming guide for fiesta and use a different remote for it. Problem should be fixed now.
the programming is not in the remote, it is in the controller in the car. The remote is only designed to give off one signal while the car will accept up to four.