PreserveVisual doesn't appear to work with nested lists

Fuse 0.35.0 (build 10867)
Tested in preview on MacOS and on iOS

First I render the initial list, then (after 2000ms to make it obvious) I insert some rows to the top of the list to allow scrolling up and scroll triggers to activate.

I would expect the scroll position to remain the same, but it moves.

This is still an issue with the latest release and a blocker for me to release improved sticky header using PreserveVisual and expressions.

Fuse 0.37.0 (build 12471)

iOS build:
Uno 1.0.7 (build 5323) OS X 10.12 i386 341576c

When playing around it appears that the bug only manifests itself when adding sub items to the sticky header container currently at the top of the page.

PreserveVisual only considers the positions and sizes of the elements inside the StackPanel, not of their children. It chooses a fixed element depending on the alignment of the StackPanel (default to Top in this case). It takes the one positioned closed to the anchoring location.

There’s not yet a way to influence this selection, or preservation process, unfortunately.

I will look into how I can flatten the list. The tricky part is figuring out the height of the content when there are multiple items with each sticky header.