Any deed, mortgage or other instrument purporting to convey, mortgage or encumber a unit ownership estate, or an interest in a unit ownership estate, is effective only as to any unit in the unit ownership estate in which the maker of such instrument owns an interest of record at the time such conveyance or encumbrance is received for filing by the county clerk, provided, a purchase money mortgage shall be deemed to create a valid lien upon such of the units described in the mortgage as are also described in the concurrent conveyances to the mortgagor. Such instrument shall not impair or otherwise encumber title to any interest in the unit ownership estate not owned of record by the maker thereof at the time of such conveyance or encumbrance.