To reproduce:
1. Open attached Unity project "Starship Voyage.zip"
2. Open "title scene 4" scene
3. In the hierarchy, navigate to Scene Root --> Canvas --> Main Menu --> Layout
4. Switch order for Load Game, Settings and Exit Game Objects
5. Go into Play mode
6. Inspect order of the layout group

Expected result: Order of the layout group should not change on starting Play mode
Actual result: On clicking play, these three objects are going back to their specific place in order. However, Main Menu Button, Main Menu Button (1) and Main Menu Button\New Game are not changing their place in the order despite being an instance of the same prefab.(see attached gif "layout.gif")

Note: Prefabbing these three (Load Game, Settings, Exit Game) objects and instancing them back into the layout group stops them from rearranging on Play (see attached gif "Prefabbing.gif")

Reproduced on: 5.5.4p2, 5.6.4p1, 2017.1.2p2, 2017.2.0f3, 2017.3.0b6