12.Purchasers at certain sales and persons claiming through owner bound by instrument executed by owner.- Every person who purchases, at a sale for arrears of land revenue or any other public demand, any land on which is situated a monument in respect of which any instrument has been executed by the owner for the time being under section 5 or section 6, and every person claiming any title to a monument from, through or under, an owner who executed any such instrument, shall be bound by such instrument.