Just found an interesting one. Obviously, if you fly SYD - MEL - BNE - YVR in PY Flexible for 6000+ CAD, you can get instant upgrade to J for your BNE - YVR segment. However, if you purchase your BNE - YVR directly in PY Flexible for merely 3000 CAD, you will be waitlisted.

Guess the eupgrade algorithm gets a bit ridiculous here since the first itinerary is not very sensible ...