VH-OEE is back in service (and has been for a number of days) and operated QF 12 LAX-BNE-SYD today (Fog diversion).
QF 31 had a scheduled delayed departure ex SYD (on 22/06) as a result of maintenance requirements (thanks to VH-OEE). QF 31 was simply renumbered QF 231 on this particular day.
Flight was re-scheduled a number of weeks ago and PAX were made aware of the delayed departure time.
On a related matter, with -OEE being down, both the flights mentioned by Singapore_Air (where is the Ltd. huh?
), in particular QF 31/32, have been affected due to tight scheduling and the 744 fleet being used to 'the max'.
Rgds