I think you are misunderstanding.
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Right now there is no way for an average user to force the client to only used confirmed change in new transactions even if they wanted to, other than manually wait and make sure they have no unconfirmed change outputs before sending funds.
I see what you mean, you are right. Would a simple configuration option whether to show unconfirmed inputs in the balance do the trick? No may be the default option, and you can always go to the console and temporarily force the opposite behavior if you want to. It may not even mess up how QT client handles the blockchain, just how it calculates the balance.
Edit: I have to check how it is this done right now in the code. I'm not positive how the balance is calculated.