Andrew and Patricia own one dwelling, which is their main residence. They decide to purchase another dwelling, which they will use as their main residence, but decide not to sell their previous main residence immediately. At the end of the day that is the effective date of the transaction, they own two dwellings and have not replaced their main residence, so the ADS will apply. They make an LBTT return and pay the LBTT and ADS due.
Two months after this purchase, they sell their previous main residence. As Andrew and Patricia have disposed of a previous main residence within 18 months of purchasing their next main residence, they will be eligible to claim a repayment of the ADS paid. They can claim the repayment by amending the original LBTT return.