Closing an application in full screen leaves a black box in Mission Control I have a MacBook Air with OS X EL Capitan 10.11.6, when I use an app like Safari or email and so on, in fullscreen mode the app work very well. But when I close the app and restart the mac I see this: 

or



Thank you for your help.
I read this and it seems to be a problem occurring when CMD+Q is brutally pushed to close a not Apple App.

Substantially, I suppose it should be a bug of the program that you are closing and so – maybe – you have to wait a bug fix update from the developer of the App in question.