This thing takes place at somewhere 3am at Londa for 12780 so never observed it but for 12779 i have seen it is like train arrives at Londa with GY Alco which reverses to other end removes the VSG-UBL/SBC coaches after that Pune twins with the UBL NZM attaches them in place of UBL/SBC slip coaches so this way reversal takes place at Londa Jn.