There was another post on the same subject a month ago. The same thing had just happened to me with a pair of New Balance walking shoes with the same kind of poly sole, the heel section literally crumbled to pieces while I was out grocery shopping.
They were marked as Made in the US, so the country of origin probably doesnt matter. I was swearing up and down at those cheap $*@!?!!! Chinese manufacturers all the way through the checkout line and until I got home, then I looked at the label.
I dont know if the "twist test" would show problems with the heels. Maybe putting firm pressure on the center part of each heel might show if theyre starting to deteriorate?