you are setting zero fees to the client but it sends a fee without telling you.
I don't know of any versions that did that.
The most recent version (v0.3.24) will pop up a dialog box that says the transaction fee is required and will display the amount.
its not only the fact that there is no FAQ
Added.
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http://en.bitcoin.it/wiki/FAQ#How_much_will_the_transaction_fee_be.3FPlease know that the client cannot say something like: the fee for getting this transaction processed in the next block is N bitcoins.
That is because there is no set fee. When the client comes up with a number, it is only making an estimate. It is up to the miner to determine whether or not to include a transaction. The higher the fee, the more likely the transaction will get included. Even a high fee though is not a guarantee.
Currently, the 50 BTC reward is adequate for many miners so that is why you will see transactions with no fee in many of the blocks yet.
It could however give an average fee/kb for the last 10 blocks or so.