Do you think mining pools are holding the transaction for days -- and thus rejecting conflicts -- even though they're not willing to include it in blocks?
The backlog has been fairly light lately. I suspect it is more likely the transactions were outright rejected by the p2p network and they never even made it to the miners.
Do they show up on blockchain.info and blockexplorer? How about some txid's? Folks might be able to give you some definitive answers with some details.