sorry if this is a stupid question but the few cars I have worked on with disks at the rear also has drum brakes for the hand brake, the disks were for the foot brake!

Is this so with the fiesta?

If this is the case as the disk rotor cooled it would tighten against the shoes.

If not and the hand brake worked with disks as well as the foot brake ther ewould be some loosening as the disk cooled.

HOW EVER, hand brakes are normally connected to the brake by a steel wire under tension , this has give in it and would more than take up any slake caused by cooling.

Hydraulics don't, one of the reasons they are more effective than wired brakes. (the better push bikes even use them now because of this!)

hope this helps