Anyone like to put forward a theory as to why this valve failed?

Some backgronnd:

Hemi Mopar/Edelbrock heads.
Comp Cams 925 springs,10 degree retainers, 10 degree locks and Hemi lash caps.
Comp 230/238 hyd roller cam and Comp hyd roller lifters.

The failure happened after about 2 1/2 hrs dyno run time. After removing the valve covers we found a lash cap had come out and the roller wheel was running on the collet.
At first we thought the lash caps had been bottoming out on the collet but after examaning other valves (which all have some degree of lock groove failure) we discovered that the lock groove was getting eaten away allowing the collet to ride up the valve stem and push up the lash cap.
We were lucky to catch this before a valve dropped!

Any help would be apreciated!

Tim