With regards to QF Link, I believe you wont be able to choose a specific seat as they are allocated for weight distribution (due to the smaller nature of the planes).
With regards to my BNE-MEL-BNE tomorrow, booked yesterday. At no point yesterday would it accept my choice of seats, always coming up with an error message.
BNE-MEL is Red E-Deal, and yesterday it was showing 4C as the only free seat available in 4 (but It wouldn't accept my request). OLCI at T-24 this morning, allocated 5A, even though 4ABC were all free (Seq# 5). Selected 4A.
MEL-BNE tomorrow afternoon, Flexi-saver ticket, yesterday morning was showing 4D only free seat until row 7. Yesterday afternoon that seat had disappeared. OLCI at t-36 (due to return flight on same day), only seat available to me is 7A, 8A or something in row 9 and back (ie only 2 free seats out of the first 30 seats!!).