Pyrex is definitely a treated glass. It's used worldwide in many different applications that require heat. Sure, dropping it can cause hairline cracks which are virtually microscopic, then heating and cooling can cause weaknesses. Can you be sure that the postman didn't drop it? (At any point? From the sellers warehouse to the postal depot, then from there to your home?). Advertised as Pyrex? Are there any product numbers/stamps on any of the packaging to verify this ( if there's not, then it's false advertising). There's too many variables here. Could you post a link to the product, and also post some pics of the packaging ?