have you checked the fronts? when you're looking at seized calipers, don't direct your attention to the side that's locking, focus on the side that's not.
check sliders primarily, then pistons. if you don't have the M springs on the back (1.6s only have 1 per side) you may find the pads crack off. mine do it when the disc's been wet and my brakes are fine.
slider pins should be bright, shiny and well greased. if they're not, they want replacing.