SQ are posting following on their website:
Notice for passengers booking on SQ285/SQ286:
We are operating these 2 flights with a leased Boeing 747-400 aircraft
and would like to inform you ahead of time, that there will be some cabin
differences. However, we are pleased to inform you that the product
offerings in all three classes onboard the aircraft are comparable to what we
offer in our own Boeing 747 aircraft.
(SQ285/SQ286 is the SIN/AKL service). Looks like they are shuffling aircraft around a fair bit.