The Pope's personal charity toward him should not be mistaken for approval of his false teachings, any more than hearing a prisoner's confession should be confused with the condoning of murder.
Now if Kung were an parishioner refusing to pay the church tax he might not have been dealt with so kindly.
Kung is like the priest/U.S. congressman Robert Drinan who worked so hard in support of abortion. He'll be criticized but not too harshly.