While heat treat probably has something to do with it, it's probably also got a little bit to do with an improperly radiused corner.
When heat treating, sharp 90 degree corners can be notorious for being the areas that cause problems. Proper radius in those sharp corners can go a long way in making the part have any sort of longevity.
Heat treat aside, it's still a bad thing if the corners aren't properly relieved and cracks can develop at those sharp corners when exposed to force/pressure. High quality parts used by engine builders often have nicely radiused parts in the hopes to overcome these sorts of problems.
As for Springfield, this is not the first time I've heard of this happening either. I also hope Springfield's customer service has come a long way since the last time I heard of somebody needing to send their gun back for service. One person I know had their gun go back 3 times before they were satisfied that everything was in order with the gun.