this bitcoin address contains transactions which may be double spends. You should be extremely careful
One of the transactions was rejected by blockchain.info and one got through.

There was a "malleability attack" going on just recently, that's probably the reason.  The attacker can take legitimate transactions, change the transaction ID (hash) and republish the transaction to the network.  See more at https://en.bitcoin.it/wiki/Transaction_Malleability - there is a BIP 62 in the pipeline dealing with this problem.

The attack is merely an annoyance, the recipient will never get twice the amount (800 mBTC in your case) through a malleability attack.