Help! Tried sending bitcoins to myself and they disappeared I'm using the bitcoin-qt client on v0.8.1-beta on Mac OSX

I have 3 addresses.  I tried sending .01BTC from one address to another.

1K3BjT1y2X2v3PGhqHh33dRb6kVGdR5CBA ->  1MattHdtuFSof3ctrZhTGzsfQecQBso2nw

However!!! When I lookup the transaction ID: f638b5ecda8d8b0280a49f342e6cac13560917d5e678f1e3b9a7f35f69b15b97

I did sent the .01 to myself but it also sent
1.2594786 BTC -> 1Ypzoqn4BYSbgeqPJ3mSPdqBC8JGzgX4r

I have no idea what the 1Yp... address is!!

What happened!!!  Did I just loose $1000 ?

it did NOT prompt me about paying any transaction fees!!

I would greatly appreciate any help! 

Update:
Yeah!!! I recovered my coins.   For whatever reason bitcoin-qt generated a new private key but didn't show ANY indication of this in the GUI.  This may be because it was backlogged by about 100 days in downloading transactions..  not sure.  but in any event LUCKILY i had been messing around with trying to migrate to multibit.. anyway i tried to export the private key and was successful:

walletpassphrase  120
dumporivkey 1Ypzoqn4BYSbgeqPJ3mSPdqBC8JGzgX4r

Then it worked !  it actually dumped the priv key and I was able to import into blockchain.info and get access again.  Not sure what happened but it was very unnerving...   again, the GUI does NOT show 1Ypzoqn4BYSbgeqPJ3mSPdqBC8JGzgX4r as one of my addresses...

Anyone care to explain what happened?

Source:
What you are seeing is a "change address".  When you send an amount that is less than you originally received, it sends the whole amount, and returns the difference to your wallet as "change".  This change may not be spendable until the transaction is confirmed.  The change address is different each time, which makes it harder for a third party to tell for sure how much is sent to which wallet.  If you are not interested in privacy, you can use a different wallet (such as Electrum) which has an option to not use change addresses -- in that case the change would go back to your original address instead of to a new change address.