It is still an area where there is no Schengen harmonisation.
It depends on the bilateral agreement that Australia has signed with the Schengen country you intend to visit and the interpretation given to it. Some may request a visa because you have spent already 3 months in the Schengen area, other not. Some may request an exit stamp on you passport.
Therefore you have to ask the Australian embassy, which should know, or the consulate of each Schengen country which you intend to visit.