This failure is an anomaly. Damage was the result of a jack knife, at speed, traveling downhill.
Jack knifing exerts tremendous strains on the coupler even when done slowly. Typical damage looks like this:
I am a big fan of the Lock-n-Roll hitch, and have been using it for 5+ years without ANY problems.
Just to be clear though, the Lock-n-Roll hitch will bind every time you jack-knife the trailer, regardless of how fast or slow you complete the maneuver . I have a couple of pictures that I will post up tonight to help visualize the binding issues, but like Martyn said, it's is just part of the design. Until you get past 75 Deg. or so, the binding is minimal, and the unit will pull out of it without much or any fatigue on the hitch, but if you go past 75 Deg turning, it will bind and damage the hitch when it straightens out. I routinely jackknife my trailer during my setup, but I will extend my tongue jack with a wheel on the bottom to release the binding allow me to pull straight without damage to the hitch. Pictures will show this better.
Also, Martyn said that all couplers will do this, and I disagree. I don't think the treg-type couplers from Australia will bind in this way... But it's been a long time since I've look at them.
Don