Well, that "not accepting backorders" policy was placed in effect in January of 2013, over a year ago. So they're still trying to work off orders over a year old? Seems unlikely, but I guess it could be true. I've never called them to order because the powder I want is never listed as "in stock". So calling in to place an order for powder not "in stock" would be asking for a back order which they say they're not accepting.
Decided to call PV and they confirmed that orders have to be entered through the web site and no back orders are accepted. This can get ugly when you try to amortize the hazmat fees. Suppose you can only get one container of powder, that'll make it much more expensive or you go without.