If I understand it correctly only someone who has previously "blinded" the coin can later exchange it for someone else's cash, using the secret information he used to blind the original coin. If only the miner knows, only the miner can later redeem it, or he has to transfer it to someone else, in which case it is no longer untraceable.
Hmm, I can´t see how it can be relevant to anonymity if a miner commits something out of thin air (generates coins) rather than having it pegged to some backing coin coming from an address. Let's say the miner commits a coin he himself generates, in the example of the paper. Why should he not do it all himself rather than first generate it and then wait to blind it in a transaction for the next miner to include in her block?