Changing the focus to another application and back to Unity, causes some UI elements in the scene view to disappear. This includes images and texts, but interestingly not all images disappear.

Reproduce:
* Open provided example project
* Open Assets/Scenes/Menu_Main/Menu_Main.unity
* Enable 2D mode in scene view
* Double click "Menu_Main" GameObject in Hiearchy window
* Focus another application, eg open Microsoft Notepad
* Switch back to Unity by clicking in the scene view, while Notepad has the focus
=> Observe a few images/texts disappear in the scene view

Expected:
UI elements in the scene view should not disappear when changing the editor focus.