So, for arcane and complex reasons I'm stuck in a holding pattern on a LAX-SYD/BNE r/t booking (basically, I'm pairing two vacations on a single reservation with about a 240-day gap between the trips; the net result is actually two around-the-world trips due to how booking one of them shook out). In the meantime I've been punching about and seeing where the fares fall, and they've been banging about like a Cessna in a thunderhead with day-to-day variations of about US$2000 for the trip (in the last 20 days I've seen everything from about $3800-6200 for broadly similar trips, including somewhere in the mid-$4000s earlier this week versus $6200 tonight).

Is this sort of banging around normal? Is there any discernible rhyme or reason to it?

Edit: This only seems to be at issue with r/t reservations. At one point an r/t was actually cheaper than an o/w, but that's (presently) not the case.