Rich:

The agent told me that they would not count a connection in a continent if you connected there on an international segment.

For example, flying from SYD to LAX on CX via HKG is OK, even if you have already been to Asia and used up all of your segments there. You cannot stop over in HKG though.

For your concern, I think you could fly QF from SYD-SIN-LHR and then return to Asia without the connection in SIN counting for anything. Again, it must be a connection not a stopover.

Of course nothing seems to be written in stone...