'25.—A person shall not acquire any estate or interest in land under a disposition specified in subsection (2) or (2A) of section 24 after the date on which registration of ownership of the land becomes compulsory in relation to the disposition unless the person is registered as owner of the estate or interest within 6 months after the execution of the disposition or at such later time as the Authority (or, in case of refusal, the court) may sanction in any particular case, but on any such registration the person's title shall relate back to the date of such execution, and any dealings with the land before the registration shall have effect accordingly.'".