apparently, when you use more than 1 address as input and hit less than 1 KB transaction size it doesn't deduct a fee. Is that behaviour intended?
Yes. In "Preferences" you can set up a default fee per kilobyte if you prefer it to include a fee even when it meets the "free transaction" requirements.
Will my transaction be confirmed?
Almost certainly. However, it may take a few blocks longer than if a fee had been included.
Thanks for the info. Finding out about this with the transaction in question of all really bugs me though, because the payment provider used (CoinPamyents.net) needs me to get the transaction done and confirmed in a 3 and a half hour time frame. Well I guess I'll just cross fingers that I don't have to put up with any sort of customer support people ...
Edit: Sadly the transaction is still unconfirmed and thus the payment was cancelled and I have to deal with support of two parties :-(.
Imo this is something that should be changed/fixed. If the reference client is designed to make certain transactions free of charge because they aren't causing much stress to the network (I guess that is the rationale behind it) then the network shouldn't "punish" such transactions by confirming them slowly or there should be a mandatory fee for any kind of transaction and the blatant lie about how transferring money via bitcoin comes completely free of any fees should stop being spread.
