I don't understand what happened there? If he sent 1 BTC to himself, then the other 8999 should be sent to a change address for which he controls the private key. That is how the deterministic wallets work today. It is not necessary to re-backup a wallet after every transaction, right?

If that is not what happened, how did the wallets back then work? Would they generate a new change address at the time of sending? In which case there was no record of the private key?