User blog comment:ShiShiPaw/Some treasures can be obtained twice/@comment-25700556-20141213103916/@comment-24956068-20141213163341

No, they do not stack, but just giving you more than one chance to get the reward. So, if you have 2 same treasure with each 50% chance, they will not make 100% chance. You still have 50% chance but you "takes the draw" twice. You may not getting at all, but you can also get more than one.