[BUG] Scroll position change when prepending one item of unknown height with increaseViewportBy

[danielsantiago]

Describe the bug
When you are at the top of the list, and you prepend a new item with an unknown height, the list is changing the scroll position.

Reproduction
https://codesandbox.io/s/sandpack-project-forked-gzs242?file=/App.js

To Reproduce
Steps to reproduce the behavior:

1. Go to the sandbox
2. Click 'prepend'

Expected behavior
When prepend there should be no automatic scroll changes.

Screenshots
https://github.com/petyosi/react-virtuoso/assets/619122/8dfcfe79-7795-41f4-bdf4-cff5ace6d2b2

Desktop (please complete the following information):

• OS: MacOS
• Browser: Firefox, Safari

Additional context
If I remove increaseViewportBy then it works the first time I do prepend, but if I then manually scroll to the top of the list and do prepend again, then it fails even without defining increaseViewportBy.

[danielsantiago]

For reference, I did a hack or workaround adding a ResizeObserver before doing prepend to do the correct scroll top calculation.

https://codesandbox.io/s/sandpack-project-forked-sqjxcj?file=/App.js

[petyosi]

Confirming, the problem is related to increaseViewportBy. This should work, I will look for a fix.

[dinhtheloc]

Has anyone got a solution to this issue?