I had one thing that annoyed me the other day: trying to book a work trip, MEL-TYO and back from HKG to MEL. Travel policy allows me to travel PE, so of course on the QF nonstops on A330s there is no such thing... A year-and-a-half ago I did the same trip (QF79 out and QF30 on the return), but in a Y/J combination that was (1) comparable in cost to a PE round-trip via SYD or HKG, and (2) therefore got approved from work.
So while it's normal that you can't book mixed cabins online, I had our corporate TA try and she said this is no longer possible due to "Qantas system restrictions". Within available fare classes it should have worked out around $2.6k, but best she could do was one-ways adding up to $4.8k (I could have booked both flights plus CX TYO-HKG in between all in J for less than that). Very annoying, now flying via Sydney in PE instead.
So while it's normal that you can't book mixed cabins online, I had our corporate TA try and she said this is no longer possible due to "Qantas system restrictions". Within available fare classes it should have worked out around $2.6k, but best she could do was one-ways adding up to $4.8k (I could have booked both flights plus CX TYO-HKG in between all in J for less than that). Very annoying, now flying via Sydney in PE instead.