That type of damage doesn't happen just by putting the bucket onto the machine. It happened after the bucket was installed, and I will bet that the damaged bucket wasn't intended for the machine that it was installed on, and the machine it was installed on has a lot more horsepower than the machine that the bucket came off of. If you were backdraging with down pressure that would account for the damage. The larger the machine the heavier gauge of steel the bucket is made of. Heck, someone could mount a BX bucket on another machine such as a B tractor, and damage that bucket because it wasn't designed for the B tractor.
It is like the kid that builds a 500 HP engine and installs it into the car only to blow up the rear differential. The differential was built for the 360 horsepower engine, and it couldn't stand up to the 500 horsepower engine. With cars and tractors, everything must be matched to work together otherwise damage occurs.