The logic in RenderAnimatedSize is buggy. It begins animation even when the target size is the same as the starting size. This causes AnimatedCrossFade, which uses it internally, to always animate even when the fade animation is finished.

To reproduce add a few AnimatedCrossFade items in a ListView.builder and scroll back and forth. Observe in the performance overlay that when an item is detached and reattached it triggers noop animation frames for the duration passed to RenderAnimatedSize and also triggers unnecessary child layout.