Slic3r (https://slic3r.org/) is the first app I've seen do this on Elementary. Basically it's showing 2 titlebars. Any suggestions?
- When the window is not fullscreen, you can see an application window with some of the desktop wallpaper repeated in it, then a smaller nested application window inside of it
- When the window is fullscreen, the desktop wallpaper duplication issue disappears but there are still 2 titlebars displayed.