After hearing from 52cartes via Facebook, I decided that there's too many questions about this deck and did some research. I just got off the phone with Tiffany Mahan at USPC about this deck.
She stated that while it's possible that someone may have printed a bogus run, this was indeed a USPC-made product, probably for an international customer. There was more than one print run of it, and the last she's aware of was in 2008. The lack of legal text on some of the box flaps is consistent with the company policy that was in effect at the time, so boxes with the legal text are probably from a preceding print run.
Assuming that a counterfeiter didn't make a copy of this deck recently, the quality issues that people are now experiencing are more likely due to improper long-term storage of the decks under excessively warm temperatures. It would affect the cellophane wrapping and the cards themselves negatively.
If you have any issues regarding a Pandora Vine Backs deck you've received, she stated that she'd be happy to look into the problem, and requests that you mail the deck(s) in question to her:
USPC
300 Gap Way
Erlanger, KY 41018
UNITED STATES
Attn.: Tiffany Mahan
I consider it very unlikely that some counterfeiter would make copies of an relatively-unknown deck like this when so many riper and more valuable targets abound, and the simplest explanation in this case is probably the correct one - it's an old deck that sat in the back of a hot warehouse for too long. I'm still interested in getting some for myself, but not at the outrageous prices some shops have been charging. We have guys right here on the Discourse selling them for under $10 a pack, some for way under.
Nathan, that site you found doesn't appear to be the Maxwell Playing Card Company. It appears to be a northern European online shop that simply chose to list the item with the company name that appears on the side of the box. Tiffany said as much when she saw it.
EDIT: I want to give a big thank-you to
52cartes (Google Translate English version
here)- he was the one who brought this to my attention in the first place and motivated me to track this problem down and get answers.