Might be a bit early for congrats as this was only a test run before hopefully booking next week but you have put your finger on the major problem - MEL-DOH!Well done.
How many J seats did you get MEL - DOH .
Up to now, more than one has been near impossible.
Also, the only other OW carrier serving KEF is FINNAIR -daily.
Trouble is that J seats are hard to come by in advance with AY but JAL serve HEL so AY kef-hel on AY then onto Japan on JAL would be doable.
I had managed to do each separately (just a reminder for those coming in late it's for myself and my daughter travelling together to LHR and separately afterwards) and found flights. But then of course last night trying MEL-DOH-LHR for 2 pax and nothing!
I was hoping someone here might be able to help but sounds like it is a common problem and I presume even if I do the bookings in 2 separately browsers from 2 accounts one will fail?