I'm pretty certain you are right about the 'blow-out'.I am not sure on the genetics but I do know people who have flocks that do not have just pullets and they lay double yolkers. Maybe its like humans in that it may run more in one strain than the others. I do not want them. I am sure they would blow out worse.
I consider it a very serious fault in a laying flock and do what I can to breed away from it.
Anecdotally, I think I'm making progress.