Where did you come up with this nonsense? It does not mean that at all, never has.

Sede Vacante = The Latin term that is used for when the Pope dies or resigns and a successor hasn't yet been elected, the phrase means "the seat is vacant."

It does not mean because the pope is a heretic we have no pope, it does not mean that everyone should slander the man who is actually occupies the seat, nor does it encourage anyone to condemn as heretics all those who disagree.... it's a phrase that has been maliciously usurped by sedes to mean all of this, but only to some sedes.

In our times of the Crisis, the Latin term "Sede Vacante" is used by the Sedevacantists to refer to the situation that I described. They believe there is a heretical usurper in the See of Peter. So, according to Catholic teaching, the See is Vacant because a heretic automatically loses his office/jurisdiction ipso facto (assuming that he was ever legitimately elected to begin with). 

It doesn't surprise me that this seems like nonsense to you, Stubborn. You don't care what the actual Catholic teaching on these matters is. You prefer to use Old Catholic heresy as your guide. Just admit that fact and stop pretending. 

It is not Catholic to believe that a papal claimant can be both a legitimate Pope and a heretic at the same time.

In our times of the Crisis, the Latin term "Sede Vacante" is used by the Sedevacantists to refer to the situation that I described. They believe there is a heretical usurper in the See of Peter. So, according to Catholic teaching, the See is Vacant because a heretic automatically loses his office/jurisdiction ipso facto (assuming that he was ever legitimately elected to begin with).

It doesn't surprise me that this seems like nonsense to you, Stubborn. You don't care what the actual Catholic teaching on these matters is. You prefer to use Old Catholic heresy as your guide. Just admit that fact and stop pretending.

It is not Catholic to believe that a papal claimant can be both a legitimate Pope and a heretic at the same time.

In our times, Sede Vacante has a universal meaning, iow, it means the same as it has always meant, except to sedes. To say it means something else IS nonsense. To say it means what you said, is to change it's meaning to suit your purpose. It's not rocket science.

You are the one who does not care what the Church teaches in this matter. There is no good reason, in fact, there is absolutely ZERO reason to go contrary to what St. Francis said in the OP - far as you're concerned, to leave it up to the Church is heresy. 

It is not Catholic to decide the status of popes, never has been, never will.

Besides avoiding giving me a yes answer, you go against what St. Francis said in the OP.  The Church makes the legal status of vacancy for "the see" not the pope. Those who do so already morally and positively determine the man is not a pope. Perfectly Catholic to do, and in fact a duty. Read the OP again.

Point out where it is our duty to "positively determine the man is not a pope."

From the OP:
"when he is explicitly a heretic, he falls ipso facto from his dignity and out of the Church, and the Church must either deprive him or, as some say, declare him deprived, of his Apostolic See, and must say as St. Peter did: let another take his bishopric"

Point out where it is our duty to "positively determine the man is not a pope."

From the OP:
"when he is explicitly a heretic, he falls ipso facto from his dignity and out of the Church, and the Church must either deprive him or, as some say, declare him deprived, of his Apostolic See, and must say as St. Peter did: let another take his bishopric"

Look at the clause just before the one you highlighted. He falls ipso facto from his dignity AND “out of the Church.” That is said first. That automatic “fall” is primary. Canon Law says exactly the same thing. 

Then, secondarily, the Church must either throw the bum out by force “deprive him” or, if he voluntarily vacated the premises, the Church “declares him deprived.”

Why is the second step mentioned? Because the Church must elect a new Pope. So before the election, the Church legally declares that the See vacant. The See did not become vacant because they declared it. It was vacant ipso facto. The Church simply formally expressed its agreement with the reality of automatic vacancy. 

The Church must declare the man deprived of his Apostolic See, because he is no longer pope. As in, the Church is compelled to do so. The Church cannot allow a man to pretend to hold the Apostolic See.

This isn't saying he is still pope until declared otherwise, it is saying that the false pope cannot be allowed to illegitimately hold the See. If he was still pope until declared otherwise, then he could never be declared otherwise..because the First See is judged by no one

This is saying the Church must declare the man deprived of his Apostolic See because no one else can do it.