First of all it's called Ascension.. (because the ranks of cards that share the same type ascend, or are risen each time played.)
This isn't a bug.
Go with a full Beastman deck (or Garlean if you have 60+ cards) so each time you or your opponent plays one, the others in your pool slowly grow. (The npc you're referring to's named Indolent Imperial whom does play a few Beastman cards along with his Garleans)
I'm currently at 47 cards so couldn't go Garlean, but you can make a very effective Beastman deck already at 30 cards (unlocking the first rank restriction on your deck);
My deck, and pardon if even remembering these right was like this:
Amaljaa, Frixio, Memeroon, Ixali, and Mutamix works 95% of the time for me.
There are other decks out there that i'm sure are closer to 100%.
Maybe you just need to collect more cards before you can effectively get consistent wins against this guy.
Def not a bug tho! ^^
added:
http://forum.square-enix.com/ffxiv/t...al#post2807357