Issue with when scrolling a ListBox/VirtualizingStackPanel when hidden

[timunie]

Note

Also reproduces using 11.1.0-beta

Discussed in #15188

^{Originally posted by BobLd March 31, 2024}
I originally posted this question on the Telegram channel and was advised to create a Q&A.

It seems there's an issue with ListBox (due to VirtualizingStackPanel I think) when scrolling the list while it is hidden. I've created a minimum app that reproduces the issue, available here https://github.com/BobLd/VirtualizingStackPanelDuplicatesIssue

To replicate the issue:

1. Click the Scroll down button to scroll down the listbox while it is not visible
2. Click Toggle Menubar to show the list box
3. Get the messy result:

I originally encountered the problem in https://github.com/BobLd/Caly/tree/develop-menubar

[BobLd]

@timunie do you know if there are any plans to fix that? I'm happy to investigate the issue but would need some pointers...

[timunie]

@BobLd I think I would add some Debug.WriteLine in VirtualizationStackPanel and friends to find out what's going on. Also lookup related PRs from earlier fixes of @grokys