Victoria and Queensland are the only states in Australia where lawyers have surrendered the contract to the estate agent, so this problem seems confined only to those two states.  I have noticed that estate agents have come to regard themselves as the custodians of the "original", and that they are often reluctant to deliver originals to the parties or their lawyers.

 However, it doesn't really matter.  It is very rare that any party would be disputing the contract document itself and alleging fraud.  Usually a dispute centres on the terms and conditions of the contract.

Of course, if a party were to allege that a signature had been forged, or a document had been improperly altered etc. then a court would want to see the original, and perhaps even have the document examined by a forensic document expert.  Whoever holds the original in such circumstances could be required by the court to produce it.