Lost a Rear Axle.......Why?

I had a rear dogbone fall out during a run. I'm just curious what would cause this so I can try to prevent it again. I got into 1/8th scale cause there pretty much indestructible but this is weird.

[Gee]

A small peice of fuel line added to the cups will help keep them in place. You'll need to raise and lower your arm on the truggy as far as they go to see how much and what end (if not both ends) needs some added. You should see the dogbone almost come out of the cup on one end, add a small piece to the other end. Some don't take much, even an o-ring from a 1/8th shock can do the trick.