I think it's unrealistic to expect BA to do some root cause analysis on why someone was moved, and as far as I know they don't do it anyway. Your best chance of finding out is when you have an airport agent in front of you talking to FMU. So I would take the equipment change / SIN-SYD overlay suggestions at face value.
Originally Posted by
footballfanatic
what does printing or downloading the BPs do?
It prevents you moving to other seats. So if you hold back on that (and emailing, faxing etc) then you can watch as other seats become available and move accordingly. If you like the seats you have got then naturally you should go ahead and get the boarding passes.