Word of caution using Bitcoin-qt client and managing your own private keys

[notme]

Your savior here is called the "keypool".   By default there will always be 100 unused keys in your wallet.  When you ask for a new address, it grabs one from this keypool (which has already been backed up hopefully) and then generates a new one to stick at the back of the queue.  There is a keypoolsize parameter you can set to alter the default size of 100 keys.

I disagree. He got lucky. The "keypool" is the reason there might have been a problem to begin with.

Deterministic wallets are clearly superior.

Sure deterministic wallets are superior, unless you are generating an abnormally large number of keys or have privacy concerns.

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[BTCBlade]

Thank you for sharing you experience, now i will not be so stupid as to try messing around with private keys

[lojabitcoin]

This is, in my opinion, one of the more serious "non-obvious" problems with Bitcoin-QT for newcomers or non-experts.

Newcomer POV: "I know my wallet just stores my private key, and I backed-up my key and wallet, so I should be fine, right?"
Wrong!

It is non-intuitive and bad usability.

Bitcoin-QT could send the "change" back to the originating wallet by default, and have an option in the settings (for privacy-seekers) to send the change to another address.
As an alternative, users would be presented with the two options (and information) when starting the client.

[DannyHamilton]

Bitcoin-QT could send the "change" back to the originating wallet by default

Be careful about your terminology. Bitcoin-QT already does this.

It seems to me that you meant to say:

Bitcoin-QT could send the "change" back to the originating address by default.

But what should it do if there are multiple inputs from multiple addresses for the transaction.  Which one should get the "change"?  Furthermore, re-using addresses decreases security since the public key becomes public knowledge when you spend an output associated with a particular address. Re-using addresses also reduces anonymity.

As an alternative, users would be presented with the two options

If this is what a user wants, I thought there were already other clients that allow this.

[mintymark]

Something similar happened to me recently, which also had a happy ending. In essence my wallet.dat became corrupt and the backup I initially used was too old for a particularly large reception of bitcoins.

Luckily a newer backup existed. But this random generation of a hundred new addresses is something that happens behind the scenes, and you dont know about it.

I think its an appaling 'feature' of the qt client.

It could flash and say new keys generated, back up your wallet!! Better, it could actually do it.