Steps to reproduce the issue on stk demo-project (author):

• go to about page
• open properties->Output Channels tab and exclude the desktop channel from serving the current page
• switch to desktop preview

The servlet container default 404 error page is shown which is fine if you're on a public instance but on the author looks more like a bug and force editors to use the browser's back button to go back to Magnolia.
The same thing happens of course for smartphone and tablet channels but in that case it looks less like a Magnolia bug as the 404 page is displayed inside the mobile preview iframe and one can use esc key to go back to the authoring mode.