Bug Unity prefab variants messed up after refactoring field's names

I detailed the steps to produce the bug in the description of the video, I copy them here, too:
1. Create a new script: (0:00)
2. Create a field named fieldA: (0:29)
3. Create a prefab and set value for fieldA: (0:53)
4. Create a variant of the prefab: (1:14)
5. Change the value of fieldA in the variant: (1:21)
6. Notice Unity does recognize the change: (1:27)
7. Add FormerlySerializedAs: (1:33)
8. Rename fieldA to fieldB: (1:45)
9. Now Unity doesn't recognize the change: (2:04)

I've filed a bug report, but they said they couldn't reproduce it and disqualify the bug. But you can try this in every Unity version from 2021.3 LTS to the latest release (2023.3.7). I replied to their email with an attached package on Sep. 4, but they haven't replied yet.

Please, someone confirms it happens to you, too.

 

I don't see where the problem is supposed to be seen in your video.

You do change the fieldB value of the variant's script but then you manually revert it.

The mouse bouncing back and forth between the two windows makes me think that maybe you expect the variant value change to appear in the original prefab's script as well. But that is not even the case for "fieldA", and expected because changes to a variant don't automatically propagate to the parent prefab.

 

First of all, you can try to reproduce it yourself and see the problem.
Second, whatever the process, from 2:30, we reached the state where the variant has a different value (15) from the original (10), but Unity doesn't recognize that (the field in the inspector doesn't highlight, there's no revert menu when right click), so I can never revert the value. Now if I change the value in the variant, Unity recognizes the field has different value than the original, but when I revert, it doesn't go back to the original value (10).

 

Ah, I see, that explains it better.

 

And that's not just an experimental find, but a real issue I had when I was developing a commercial project, it took me quite some time to spot the issue and I didn't find an easy fix as I had so many variants.

Hope Unity will fix it soon

 

Indeed, I can reproduce this in 2022.3.9f1.
After renaming the field with FormerlySerializedAs the connection to the original prefab's value seems to have been lost.
It also behaves the same even if you enter prefab edit mode.

It starts working again once you remove [FormerlySerializedAs]. I'm betting that this confuses the prefab variant lookup strategy in some way.

 

yeah, actually I had some idea that it was because how they handle the attribution FormerlySerializedAs, and how they handle field changes in the variant, I had to edit the meta files, and the process wasn't comfortable. I'm afraid in the future when I refactor my code and this happen again without me noticing it. (or maybe it already happened again but I just didn't know yet )