Nothing there about the Apostolic See losing the faith, though. To quote Constantinople IV again:
since that saying of our lord Jesus Christ, You are Peter, and upon this rock I will build my Church, cannot fail of its effect, the words spoken are confirmed by their consequences. For in the Apostolic See the Catholic religion has always been preserved unblemished, and sacred doctrine been held in honorI cannot see how this solemn definition of Catholic doctrine, originally imposed upon the entire Eastern Church by St. Hormisdas and then signed by all the Fathers of the Eighth Ecumenical Council, can be reconciled with the view that the Roman Church (which is, to quote +Cyprian, the root and matrix of the Catholic Church), could ever "lose the faith", or no longer be habitually infallible in the acts of her pontiff's authentic magisterium.
I don't even know what post you are talking about. What you claim certainly doesn't sound like anything I said. It does seem a bit extraneous I'd prefer the thread get back on topic.
Do you have any specific comments on what points were actually made in the letter?