I have repaired a lot of these when I was there, the brake force distribution was ok, the problem was that the suspension completely unloaded from the rear causing rear skid, Installing the drum brake prop valve sort of masked the issue as the rear slave cylinders didnt get much juice with it.
The side skid usually experienced in corolla and civic were more because of people trying to have them aligned so the car rolled forever straight when they left the steering. The correct alignment for any RHD car is to let it drift towards the left over a distance of more than half km when the wheel is left alone. This is to account for road crown and also a safety that if driver falls asleep the car will drive itself into a ditch rather than onto oncoming traffic which would be on right side of road (if double carriage road) - this drift is setup with a slight adjustment of caster angle to make a gentle cross caster.
Have you any experience driving older sedans with leaf springs? - you will know that if you raised it up too much from rear it would back steer on bumps or axle wrap on launching hard - the same exact phenomenon here. The suspension unloads and the tires lose grip due to the missing extension travel of rear shocks.
If you did this with a heavy load in rear (3 full suitcases or 2 biryani deg in boot) - the car behaviour was favorable. Toyota indus should have never installed discs in the back either, they are not needed in "eskalai" and "2D" - its a slow passenger car anyway and stops perfectly well on disc/drum hybrid.
