I think I know where you are going with that. The more flex you get the greater the torque stress on the axle. As the bushing in the arm start to max out on their flex, the torque force on the housing goes up very quickly with any extra travel. Basically, there is a limit to how far you can have one wheel go up with the other dropping before you start to bind up the rear suspension.

Going past the binding point puts a lot of stress in the axle. Add in the torque from climbing and the housing fails.

Two solutions.

1: Limit the axle travel to stock.

2: Develop control arms with more flex.

3: Beef up all the parts so they dont crack when overloaded.