strange problem with sending BTC from my wallet, please help!

[pro-bitcoin]

Hi,

Sorry if this is not the right place to ask this question, operater(s); feel free to move this topic..

Yesterday I bought some shares in a group buy. My Bitcoin address is 1FVaqniSgLgDcTAzXm9jKcBphskWhiz6T1

See topic https://bitcointalk.org/index.php?topic=226319.0

I transfered exactly 8BTC to the Sonic with Bitcoin address 1GW2ReZrFWuMn71xy4efB3sxViPC3iF8ES

My wallet gave me the transaction ID c2988449f2b92dc0c30c2149d3ad4770e9852eafc0b84b9398c598f186f56572 , so I copy pasted this in the forum to let Sonic know my Bitcoin address en that the transaction was succesfull: https://blockchain.info/tx/c2988449f2b92dc0c30c2149d3ad4770e9852eafc0b84b9398c598f186f56572

The strange thing is that is used Bitcoin address 1BuiUmyE1p22hhFa5WUosYbrqTDgXeeSke for sending the BTC. When I click on this Bitcoin address I see my own bitcoin address, transfering 8.3995 BTC to that address.

see: https://blockchain.info/nl/address/1BuiUmyE1p22hhFa5WUosYbrqTDgXeeSke

1) How can It happen that there is a bitcoin address "in the middle" , an address I do not know ?
2) How can it happen that 8,3995 BTC is transfered , but I gave an order for exactly 8BTC ? And for as far as I can see, only 8BTC is debited from my wallet.

I first was thinking of malware om my pc, but I reinstalled my pc, took some new malware software with recent updates and it cannot find anything.

I hope Im doing something stupid here please help me out, because I cannot trust my wallet at the moment!

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[suryc]

This is completely normal wallet behavior.
You paid with your address 1BuiUmyE1p22hhFa5WUosYbrqTDgXeeSke, not with your address of 1FVaqniSgLgDcTAzXm9jKcBphskWhiz6T1

Your address of 1BuiUmyE1p22hhFa5WUosYbrqTDgXeeSke was created on April 28 as "change" for the transaction when you paid 51.6BTC to 162HWpt9njiDsk5nwGixw7fDPuNy55Kh9X. You had 60BTC and paid 51.6BTC plus a transaction fee and were left with 8.3995BTC at the new address.
 
Likewise, when you paid for your group buy, you actually paid from the address 1BuiUmyE1p22hhFa5WUosYbrqTDgXeeSke which had more than 8BTC and "change" of .3995BTC was made and returned to your wallet at a new address of 1JzQNDAWhjJ5vRJAoyYVtU2YaXDsvQt1sH.

If you don't understand this, then you don't understand the fundamentals of bitcoin transactions and I suggest you read up on it: https://en.bitcoin.it/wiki/Transactions

[suryc]

Also, just to clarify for you: the addresses where "change" is sent do not show up in your wallet in most clients.
If you want to see them it is addressed briefly here: https://bitcointalk.org/index.php?topic=184768.0

And something else explaining the reasons for this behavior:
http://bitcoin.stackexchange.com/questions/1629/why-does-bitcoin-send-the-change-to-a-different-address