I just upgraded our test environment to April 2018.
It appears that your work area will now contain images of all published apps that you can not delete. You will see the image in the top right corner to show that it has been published.
It is there forever. You can only duplicate to then get a working copy to make changes.
This is going to make for a very large work area on my screen.
Does anyone else find this to be a really bad idea?