What I've seen is the cam-ing action of the broken yokes/joint hit the bottom of the upper ball joint and it pushes the whole joint up and out.Typically what happens is the bottom gets stuffed down and the top pin just gets yanked out of the upper body.
Edit: I just went and looked at a HP D44 knuckle and am not sure how the upper pin can get pulled out. The way the knuck is loaded in place, it wouldn't allow the knuckle to go down. Please learn me something new.
Joe_and_jeep- What is breaking on your joints?