I had a previous 2003 gd series jazz, that had drum brakes at the back and front disks, no problem with the handbrake, after keeping the car for 3 years exchanged it for a 2008 gd series jazz, the brakes are now all disks, the handbrakes needs a bit more effort to secure it, as I live on a steep road, my guess is that when driving the discs get warm, and expands, so therefore you need to pull the handbrake harder, applying the footbrake first helps in reducing the effort required.