Craig owns a dwelling which he uses as a main residence. He inherits another dwelling from his parents. An inheritance is not chargeable to LBTT or ADS, so he will not pay LBTT or ADS, even though after the inheritance he owns two dwellings (his main residence and the inherited dwelling, in respect of which he is deemed to be the owner ("deemed ownership"). Craig decides to sell the inherited dwelling and purchase a buy-to-let dwelling with the proceeds.
At the end of the day that is the effective date of the transaction, Craig owns two dwellings and has not replaced his main residence. Therefore, he will pay the ADS on the newly purchased buy-to-let dwelling.