Not sure if bug or just feature but when I have a UI LayoutGroup in a prefab then all the children of that group [in a prefab instance] will have their RectTransforms marked as changed and applying the changes makes no difference - they will always be marked as changed. Does not seem to cause an issue but means the "Overrides" drop down will never be empty for such Prefabs which is a minor annoyance! 2018.3.8