I do not know the specifics, but most of the unconfirmed transactions tend to be ones in which the miner fee is not being paid since the miners will not get paid they tend to overlook those transactions. I have herd the free payments at times have taken up to a week. But really depends on where the wallet is, I would ask them. Also part of the unconfirmed transactions are ones that have been posted but no miner has added to the blockchain as in new transactions that were just submitted since the last block. I would check with the wallet creator and see if they can shed some light on why that transaction has not posted. Other reason might also be an update to the main fork, I have not completely followed the Bitcoin network in a few months as most of my coins are a an exchange and they take care of all the wallet issues on there end.