bitcoin-Qt and blockchain mismatch

Right now I am running bitcoin-qt version 0.8.5 Beta

My wallet says I have 1.76867944 BTC and this seems correct. All the transaction history looks correct.

When I look at the blockchain.info for my address in the wallet it says that I only have 1.18567944 BTC

The discrepancy seems to have occurred with transaction ID 6d49c2df910250a3cae6cbe3ed157e300de8b5cddfc0882db89980f29ca28391 back in June. In that transaction my bitcoin-qt wallet says I paid 2.0 BTC to 16qMbvYmbm7n1CPHT415DRX4JPrn3KEZHp which is correct and the blockchain transaction ID shows that also. The blockchain transaction ID also shows a near simultaneous payment of 0.583 BTC to 15yGGVTKuTmDJJVe5CgcDYW8R7htDgWgqL. I don't have any knowledge of that transaction with that wallet and the blockchain shows that address 15yGGVTKuTmDJJVe5CgcDYW8R7htDgWgqL only has that single transaction in its history. In addition the blockchain shows the Estimated BTC transacted as 0.583. That is neither the amount I sent nor the total. It seems I have lost control of 0.583 BTC. Not much granted but as I want to transact more and more in BTC I also want to feel good about the integrity of this system.

The 0.583 BTC seems to be not yet redeemed and is now 4 months old. Given the fact that I did not spend it and my wallet says I should have it. What do I do?

Any help. Thanks.