Hi,
When an airline has a transit point on a flight, (eg OS 7 VIE-SIN-MEL), I know sometimes you may not have a availability on the whole leg, but on parts you will. Can anyone explain why for particular date OS 7 VIE-MEL is showing wide open, with YBMHQX & G classes available, while for the same date OS 7 VIE-SIN, everything in economy is zeroed out?

thanks
goodo