Great question.
When the Fathers of Vatican I were defining the dogma of infallibility, they had in front of them the case of Honorius I, who was anathematized as a heretic by a council and later Popes. That happened precisely because Honorius tried to play cute with Sergius and the Monothelite heretics and didn't condemn them.
This prior example is important because it shows that "infallibility", as we define it, does *not* mean that every Pope is above reproach or cannot be personally condemned as a heretic when he fails to do his job. It just means that Christ will not allow the Pope's personal failings--under any circumstances--to solidify as official teaching. Because the Pope serves Christ as a regent of the Church, a temporary head who acts on his Lord's behalf--not as a dictator who can do as he pleases.
What you are watching unfold now toward Francis shows what we actually believe about the papacy. Francis has no power to change what the Church has always taught, and if he tries to, a) he will ultimately fail and b) in the meantime Catholics are not obliged to follow him into error and are, actually, bound to stick to the truth and correct him as necessary. St. Paul was never called Head of the Apostles and never ever took that title away from St. Peter--but he had to correct Peter's behavior when need be.
Thanks.
Headed back to bed.