This could happen with files saved before ef4aa42ea4, so before global areas
were written to .blend files.
We would just always add the top- and status-bar, even though the screen wasn't
supposed to have them. I'm not entirely sure what caused the further issues
observed there, most code should probably handle the case fine still. But
apparently something didn't.
Steps to reproduce were:
* Open Blender from before ef4aa42ea4 (e.g 2.91 release)
* In 3D View, View > Area > Toggle Fullscreen Area
* Save the file
* Open the saved file (can be in newer version too)
The fullscreen is corrupt now, especially noticable after duplicating the
workspace.
5c72a4d452