504 had many bugs...my dvr was updated to it and after that recorded content skipped randomly and it had many stabilit issues atleast in my dvr..then after complaining to airtel I was informed that they had received many complaints from dvr subscribers after they updated to 504.... so either they will release a new update or rollback to previous one. Then in Jan 2015 one day I manually updated my dvr and it was rolledback to 503.