Thank you Tim, and all who responded.
I haven’t snapped heads installing them; rather, they snapped in service. Still, I think Tim is on to something. I’ll try the new ones on one or two cars - ensuring they are only snug rather than tight - and see how they do.
The latest iteration of the Kadee has a nice appearance: slightly flatter and wider head, and matte finish as compared to the shiny old ones. Rarely any need to paint them either, of course.
Tim O’Connor wrote:
I use the Kadee screws for cases (hoppers and flats) where the length of the screw causes it to emerge--
and become visible - or if it interferes with something inside the car, like a weight. I install it, and then cut it
off flush. If you're snapping them, you're over tightening them. Use a tiny drop of Loctite if you're worried
about them coming out.