To reproduce this bug:

1. Open the project
2. Open Assets/Scenes/renderorder.unity
3. Expand HUD object, notice how it is before the back overlay and renders after it
4. Move it bellow the overlay, notice how it still renders on top of it
5. Change the Z position of the overlay to -60, notice how now overlay always renders after no matter if it is above or bellow in hierarchy
6. Remove Canvas component from Game Panel, and put Z back to 0, notice how now the render order works fine in the hierarchy, objects bellow are rendered after