this bitcoin address contains transactions which may be double spends. You should be extremely careful i sent 0.4 btc to exchanger 
and this transaction was sent 2 times from my wallet and spent to me 200$ (0.8 btc)
which i wanted only 0.4btc to send
transaction hash:
https://blockchain.info/address/15o8CfP4z8cWiZCp5euzNEqXjEFTyNF5Yb
funds are still missing from my blockchain wallet more than hour ago
and at this transaction at other place when clicking on "hash" i see:
" A conflicting transaction has been detected in our memory pool. The transaction hash displayed below may change. "
https://blockchain.info/tx/f3cf0d91fd678de0bbbf13aa69e87ab3c0e7c55c3aecb03c06ac78d5139fc2b6

so my funds are gone now? or will they come back
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.