So what do people in Australia do when they move and have to sell their house, which will happen a lot before the 30 years is up? Are the buyers stuck with the

So what do people in Australia do when they move and have to sell their house, which will happen a lot before the 30 years is up? Are the buyers stuck with the exact same terms that the original purchasers set on the remaining principal, and then have to enter a separate mortgage for the part that's already paid off? Or do there tend to be clauses that allow full repayment on transfer of ownership or something like that?