Okay, so this happened when I was in Golem Tower, enchanting some cards. I had multiple cards I wished to enchant in my hand. I drew one monstrous treasure card. After enchanting one of my cards, I was able to draw again (I had only discarded one card). I was then able to enchant all the cards in my hand with the same monstrous card, because it let me keep drawing it. After the battle, when I checked my treasure card deck, I still had five monstrous cards (I started with six). I tried it again, and the same thing happened, only this time I lost the cards I used.
You are limited by how many cards you can hold in your treasure bar. You need to create a few, log out and back in then create more and repeat. It's a long running bug. You can create more, but you have to log out for them to register before you create another batch. It's very tiresome.