I have seen shafts split during a shot, however, the only ones I have seen do this had an insert in them for 5/16-18 or 5/16-14. I have never seen a shaft like those used on a McDermott split, but anything can happen. The most common problem I have seen was with Heubler Shafts with the Nylon Insert they have used, I don't think the problem was the insert itself though.
I kinda think that sometimes the insert become loose, and the constant force applied to the joint through shooting and breaking causes the insert to act like a wedge that splits the wood over time. Another factor could be exposure to moisture, like being left in the truck of a car. I think in this case the expansion and contraction from hot and cold cause swelling which causes a shaft to crack.
JIMO