Sometimes the factories that are making the legitimate product run an off the books "Second shift" to make totally identical knock offs.

I've seen knock offs from china that are so identical they even copied the patent marking my client had molded into all their products. The knock off actually had my clients patent stamped into their product.

It's even more common in China that people that work on products especially manufacture design engineers simply walk down the street with an existing design they worked on and start their own company. Just look at the ecig business Chinese knockoffs of "western" brand designs that are manufactured in China are available before the real product even hits the market.