strange weird address in transaction after send bitcoin bitcoin-qt as an example, I have the wallet with address-A (with 10 BTC)
If I send 1 BTC to someone (address-B) then in transaction I see

address-A &gt; 1 BTC &gt; address-B
address-A &gt; 1 BTC &gt; address-C

after, on address-A I have 8 BTC, but my bitcoin-qt show me 9 BTC (as it must be)
why it makes sends to strange address-C ?
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Found an answer here https://en.bitcoin.it/wiki/Change
When you send money to another address, the client selects one or more unspent outputs to get a sufficient amount to cover the amount you are sending.  Any excess is returned to your wallet using a change address.

In your case, it looks like you had an unspent output of 2 BTC.  Since a transaction completely consumes its inputs,  the transaction needs to send 1 BTC to your specified address and 1 BTC back to your wallet to account for the 2 BTC that were consumed.

Changes addresses are typically not displayed by the client.  If you are running Bitcoin-Qt, you can check all of the addresses in your wallet by entering the command


  listaddressgroupings 


in the debug console.