All items you buy now and all singled items you bought are marked "Already yours". The problem is with the bundles like bobbler said.
We already mentioned this in another thread but either they can't change it or they first work on other tasks.
But of course you are right. It should not be possible to buy things twice. The faces... I bought all of them in the beginning. But I don't like them. I think the first you've got is one of the best.
And...
welcome Tarissa