The simple answer is that the Qantas website is just sucking on the details. Again.

Take the Finnair seats. Phone Qantas to add the QF seats. Tell the agent that the QF website is causing problems and that you want to just add the QF seats and because it's QF's website failure causing you to have to phone you don't want to pay the QF phone agent fee. I'd even try emailing Finnair and pointing out that Qantas made you cancel the seats and could you have your money back, please.