Gray,
I would say that this sounds a bit peculiar and a bit dangerous too!.
I would agree with you saying that it could have happened at the factory.
I've been on a tour through a cable factory and the flexes are made by spraying the plastic on to the pre-twisted insulated cores.
I'd say it is a tensioning problem, during manufacture.
I wonder how many more people have flexes like the pieces you have?.
