Was the mirror Erised "broken" in Fantastic Beasts?

Question

When Dumbledore looks in the mirror Erised he sees his deepest desire:

Grindlewald

But before that the mirror shows the past when

Dumbledore and Grindlewald close their "blood troth"

In the Harry Potter books and movies the mirror is never shown to show the past. Is this a plot device as they had to show that important information somehow or is it a movie fail or simply an error in continuity?

Or does the mirror show the past of the person looking into it at any other time in previous books that I simply don‘t remember?

I know, that Harry sees his parents, but again this is his deepest need at that time and not a memory / glance of the past.

As for the duplicate identification: I specifically do not ask why Dumbledore sees

Grindelwald

as this is very well answered in the other question. But I want to know why the mirror shows that specific point in the past to "explain" the desire to us spectators. It did NOT explain Harrys desire for his parent using old memories, it just showed him standing between them (although of course they looked like they did in the past as there are images that are more current than these)

One could say: The desire of Dumbledore is, to revert the troth. But then imho he would see

the vessel being destroyed

in the mirror and not it beeig created...

That's the reason for my question: Is it a movie error to show the mirror showing past events that explain the current desire of the person standing in front of it? Or is the mirror shown to behave like that in any other canon source?

Answer 1

Does the mirror show the past of the person?

That's one way of seeing it but in reality it show you your deepest desire

Harry: So, then it shows us what we want? Whatever we want?

Dumbledore: Yes...and no. It shows us nothing more or less than the deepest, most desperate desires of our hearts. Now you, who have never known your family, you see them standing beside you. But remember this, Harry. This mirror gives us neither knowledge or truth. Men have wasted away in front of it, even gone mad. That is why tomorrow it will be moved to a new home, and I must ask you not to go looking for it again. It does not do to dwell on dreams, Harry, and forget to live. src

So his desire was Grindlewald only at that moment and he see a memory of being with him, that's it.

Trivia: Erised is desire spell backwards.

Answer 2

From Pottermore:

The Mirror of Erised is one of those magical artifacts that seems to have been created in a spirit of fun (whether innocent or malevolent is a matter of opinion), because while it is much more revealing than a normal mirror, it is interesting rather than useful. Only after Professor Dumbledore makes key modifications to the mirror (which has been languishing in the Room of Requirement for a century or so before he brings it out and puts it to work) does it become a superb hiding place, and the final test for the impure of heart.

The mirror’s inscription (‘erised stra ehru oyt ube cafru oyt on wohsi’) must be read backwards to show its true purpose.

J.K. Rowling’s thoughts

Albus Dumbledore’s words of caution to Harry when discussing the Mirror of Erised express my own views. The advice to ‘hold on to your dreams’ is all well and good, but there comes a point when holding on to your dreams becomes unhelpful and even unhealthy. Dumbledore knows that life can pass you by while you are clinging on to a wish that can never be – or ought never to be – fulfilled. Harry’s deepest yearning is for something impossible: the return of his parents. Desperately sad though it is that he has been deprived of his family, Dumbledore knows that to sit gazing on a vision of what he can never have, will only damage Harry. The mirror is bewitching and tantalizing, but it does not necessarily bring happiness.

From what I can make of these passages, it seems that Albus made some modifications, before "bringing it out" of the room of requirement nearly a century ago. Harry Potter takes mostly takes place in the 1990's. An exact century before would be in the 1890's, but since it doesn't have to be exact and/or because perhaps the timeline of the Fantastic Beast films will be slightly altered, we can suppose that he may have modified the mirror either earlier than shown in the film or he may have yet to...

"It shows nothing more or less than the deepest desire of our hearts." - Albus Dumbledore

With that being said, nowhere is it stated that the mirror will not show you the past, as there could easily be something from the past that someone may desperately desire, which is what the mirror shows it's viewer.