Whenever any real property has been heretofore or shall be hereafter purchased by any county, city, borough, incorporated town, township, school district, poor district or institution district, to be called hereinafter municipality, for nonpayment of taxes or municipal claims under any act of assembly authorizing such sale, the municipality or municipalities purchasing said property may, after the period for redemption has expired, in conveying such real property to a purchaser, execute a special warranty deed, warranting the regularity and validity of its original claim or claims and the procedure through which such municipality or municipalities acquired title: Provided, however, That such municipality or municipalities shall only be bound by such warranty to the extent of the purchase money it receives for such real property.