I tested this too and happens too on my computer.
Your layout is bigger then your project size.
The pieces that dissapear are simply out of view, because the screen does not know where it should go.
If you change your layout size to the same size of your project, fixes it.
If you add scroll to behaviour to your square object (same size layout, or bigger then project view) , fixes it too.
Looks to me this is more of a design mechanic problem.