Wallet says I have 2 BTC more than when I check the balance of my public address

[editninja]

I am having a small heart attack right now. I use Bitcoin-QT on OSX (10.7.2). I decided to move a portion of my coins to a paper wallet last weekend. I did a quick test with a throwaway wallet, imported the private key to Mt. Gox, everything checked out. So I felt comfortable moving 5 BTC to a completely new paper wallet.

I verified the transaction on the blockchain and it looked fine. My QT wallet shows a 5 BTC withdrawal, which is of course what I expected. However, when I check the transaction history on the QT wallet's public address, it says that there is an additional 2 BTC debit, which adds up to a 7 BTC withdrawal. I didn't send 7 BTC to my paper wallet. I sent 5 BTC.

I just imported the private key of the paper wallet to Mt. Gox, to ensure that the balance of the wallet was what I expected. Yes, there were only 5 BTC in there.

Basically I am afraid that the wallet on my hard drive is not giving me the correct balance. I don't really understand what change addresses are, but could that have something to do with this? I'm confused. Why is the blockchain telling me I have 2 BTC less what Bitcoin-QT tells me I have?

[RW02]

paste the bitcoin address here and lets see.

[PenAndPaper]

If the 7 btc was from a sinlge input then the 2 btc probably went to change address. You still have them in your wallet but in a new address.

What impresses more is this though :

I just imported the private key of the paper wallet to Mt. Gox, to ensure that the balance of the wallet was what I expected. Yes, there were only 5 BTC in there.

You are making a super duper secure paper wallet and then you import the private key to mt.gox. wtf?

[wearepoor]

Basically I am afraid that the wallet on my hard drive is not giving me the correct balance. I don't really understand what change addresses are, but could that have something to do with this? I'm confused. Why is the blockchain telling me I have 2 BTC less what Bitcoin-QT tells me I have?

Very likely, but only if you sent coins from Bitcoin-QT wallet

[DannyHamilton]

I don't really understand what change addresses are, but could that have something to do with this?

Yes.

Why is the blockchain telling me I have 2 BTC less what Bitcoin-QT tells me I have?

Because a wallet has multiple addresses.  Blockchain.info (which is the name of a website and is not "the blockchain") is only telling you the balance of unspent transactions that you have received at one address.  The rest of your balance is held by your wallet at some other address.

If you want to see the full list of unspent transactions that your wallet has received and what addresses they have been received at you can type the following in the "Console" of the "Debug Window" found under the "Help" menu.

Code:

listunspent

[editninja]

If the 7 btc was from a sinlge input then the 2 btc probably went to change address. You still have them in your wallet but in a new address.

What impresses more is this though :

I just imported the private key of the paper wallet to Mt. Gox, to ensure that the balance of the wallet was what I expected. Yes, there were only 5 BTC in there.

You are making a super duper secure paper wallet and then you import the private key to mt.gox. wtf?

Maybe I'm missing something in terms of how private keys work. I'll never use the paper wallet I just imported to Mt. Gox ever again. As far as I understand, paper wallet imports are one-time, entire-balance transactions and then the paper wallet is essentially useless. Why would it matter that Mt. Gox has a private key that I will never use again?

[PenAndPaper]

I 'm just pointing out the contrast in terms of security between keeping bitcoins in an online exchange and a paper wallet.
Other than that i didn't even knew that you can import addresses in mt.gox. I mean mt.gox is an exchange not an online wallet.