I'm looking at the option of changing an upcoming SYD-BNE flight to a day later as I'm now able to stay an extra day. The original booking is 2 one ways on a single PNR both getaway fares which have an $80 change fee and the fare on the new flight is about $20 more than the original (can't see anyway to check what it was exactly). However when checking the cost on the change process it's saying that the fare difference is $65 for a $129 fare (original fare I think was $109, maybe $99).

So my best guess is that the system is calculating the fare difference for both flights even though I'm only want to change one. To make things more confusing I experimented with changing both flights and the cost of changing was less than changing one!

Anyone experienced anything similar?