Item components seem to be replaced whenever new items are added to array

Nobody has claimed this yet.

I'm trying to get an understanding of what the intended behaviour is here.

I was experimenting with adding a fade-in effect to my images when they loaded by storing a boolean `loaded` state in the item which I would flip "onload".

What I found was that all (apart from a seemingly random few that didn't) of my images would fade in every time more data was loaded.

I thought it might be because I wasn't defining an `itemKey` function, but adding one didn't change the behaviour.

Do you have to provide an ItemComponent that is completely pure with no internal state that can be thrown away at any time and re-rendered?

Here's an example https://codesandbox.io/s/masonic-example-forked-ynl73q

Start with the linked CodeSandbox and inspect how itemKey and ItemComponent behave when new items are appended. Compare the observed remounting and state loss with the intended lifecycle behavior; the issue is done when that behavior is established and a focused fix or test direction is identified.

Written by the indexing model from the issue text.