Specifically, trading cards of your choice. This, of course, ruins the market for pretty much all cards if it exists. And if not, maybe this specific information will at least help track down the bug where cards of ex-nations can show up sometimes.
After checking out the ongoing sales page, I started bidding on this ex-nation card, which only had two owners, Bovidia and Destructive Government Economic System. Some time later, I noticed that a third copy of an ex-nation had been generated during the sale, for Pavakahir, who immediately threw it up for sale to undercut Destructive Government Economic System. Undeterred, I threw up a second purchase, intending to get both copies, when to my surprise, a fourth copy appeared under Korilon and also instantly went up for sale. Still committed, I bought that one as well. But I also did some digging. Both of those nations that managed to spawn the right ex-nation seem to be puppets of the same person. I won't directly name them, but a quick look at their trading histories makes it pretty clear.
I find it unlikely that two copies of a specific common card would show up within two minutes. I find it extremely unlikely that two copies of an ex-nation (which isn't supposed to spawn at all!) would do so. And I find it near-miraculous that it would be two of the same person's puppets who had it happen. I think it's much more likely that there's some kind of exploit, and that the person who controls those two nations knows how to do it.
And even if I'm wrong, two cards that weren't supposed to be able to appear in packs still appeared in packs, which is a lower priority bug, but still a bug.
EDIT: Oh, and ignore the one on GameFAQs Founder. That's one of the three that I bought, not another extra copy that came out of nowhere.