I went to the bazaar at level 21 to by the new deck i was saving for then i buyed the deck and selled my deck with treasures ( i always do this and this never happened to me what i am going to tell you ) and then i went back to make my deck once i went to treasures they were gone O: and if i did sell them with my deck its still bad because they did not give the money for selling them!
I just sold a Starter Deck with three treasure cards in it. When I checked my treasure cards again, the cards that were in the Starter Deck were back among the available cards. I repeated this two more times with the same results.