Bug in re-assignment / re-render logic

Describe the bug

Hello,

I have noticed this issue already a year ago. Please have a look into both GIFs.

Scenario: I have a list of rows, with child-rows. I can expand/collapse these rows.

Here the example where everything is fine:

Here the example where it is broken and sadly not usefull anymore:

The upper working example was done with a version before _ Rewrite view re-assignment logic_

The lower broken example was done with the latest version.

Currently, ALL items re-render and move around, if I expand a row to render its child rows. Before that, only the new child rows render and all rows below,

How does my code look like? When expanding a row, I take my list of items, splice my new child items into it (after the parent item) and at the end I re-reference my items array to trigger the reactivity in the scroller library. Thats it..

Any help with it?

Reproduction

1. Render list of items
2. shallow copy that array, splice new items somewhere in between
3. render that new array

System Info

System:
    OS: Windows 11 10.0.26100
    CPU: (20) x64 13th Gen Intel(R) Core(TM) i7-13800H
    Memory: 8.43 GB / 31.69 GB
  Binaries:
    Node: 24.14.1
    npm: 10.8.3 
    pnpm: 10.12.4
  Browsers:
    Chrome: 150.0.7871.114
    Edge: Chromium (150.0.4078.48)
    Firefox: 151.0.4 
    Internet Explorer: 11.0.26100.8115
  npmPackages:
    @vitejs/plugin-vue: ^5.0.5 => 5.2.4 
    vite: ^5.3.3 => 5.4.21 
    vue: 3.5.13 => 3.5.13

Used Package Manager

npm

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• The provided reproduction is a minimal reproducible example of the bug.