I found an interesting one a while ago, I'll try post later with the txid. Basically, I found a still unconfirmed transaction,which was initially broadcast in like 2013, and that blockchain reported was included in many blocks. Very strange.
It turned out that it was broadcast by a very old client, and very few miners still ran that version of bitcoin. but some did,and it occasionally got mined and announced. But, the network rejects these blocks since they contain a now non-standard transaction.
TXID or it didn't happen. Blocks containing non-standard transactions are perfectly valid and will not be rejected; they just aren't mined by most miners, so creating non-standard transactions is a bad idea if you don't like waiting a long time for confirmations.
From my chat logs I saw it 28th February here:
https://blockchain.info/tx/4005d6bea3a93fb72f006d23e2685b85069d270cb57d15f0c057ef2d5e3f78d2 but I guess they've purged their logs for orphaned transactions. It was for a p2sh address, I decoded the redeemscript, which was for a 1-of-1 address. Blockchain said it was unconfirmed, but it had been included in many blocks. Each of them was no longer in the leading chain.
So it looked like the transaction had an invalid signature (in terms of 0.7+ clients, the majority), although it was fine for 0.6+. The small number of people on 0.6 were the only people who could mine it, but the mining power was on 0.7 anyway.
So blockchain was right in saying 'unconfirmed', as although it made it into occasional blocks, they were all orphaned.
