Blank space appears when scrolling up in ListView with variable sized elements

[mikegoatly]

Describe the bug

When a ListBox contains variable height elements, a blank space appears before the first element when scrolling up:

When the scrollbar eventually reaches the top, the list items jump up and end up in the correct position.

I've put a simple repro together here.

Screenshots
With FluentAvalonia theme, a gap appears between the first element and the List:

FluentAvalonia.mp4

With default Avalonia Fluent theme this doesn't happen:

Avalonia.Default.Fluent.mp4

Desktop/Platform (please complete the following information):

• OS: Windows 11
• FluentAvalonia Version: Tested with 2.0.5 and 2.1.0-preview5
• Avalonia Version: Tested with 11.0.10 and 11.1.0-beta2