I've just booked two QantasLink flights as Avios redemptions and thought I'd share my experience here in case it helps anyone else trying to do it.
The flights were:
1/ Perth to Alice Springs: 10k Avios + £29
2/ Alice Springs to Sydney: 10k Avios + £27.80
It seemed like a decent value redemption as the flights would have cost ~£200 (PER-ASP) and ~£160 (ASP-SYD).
It took me two calls to the UK BAEC team to book it, the first person I spoke to said it was a codeshare and so couldn't be booked. I was better informed when I phoned back to try again and the agent was very helpful and had no issue booking both flights.
It definitely seems that it is the fact the flight appears like a codeshare that means some agents don't think they can book it.