The front axle is on a pivot, the rear axle is solid. All the stability of a tractor comes from that solid rear axle. If the rear ever comes off the ground, you are balancing on the 1 pivot pin holding the front axle on. So the tractor will start to fall to one side or the other. Jamming the bucket down provides stability & drops the rear down. So you now have the bucket & rear tires keeping the machine from falling over.
And this is why rear ballast is so important. I knew that. Violated the laws of physics and paid the price.
Rear tires are now loaded so that will help in the future.