On the Mac, when exporting an expression map to disk, the name of the file is blank.
This means that you have to type it, or select an existing file, before saving. This is a bit dangerous, since you can always select the wrong file when fatigued after a long editing.
Couldn’t it be possible that the file automatically gets the name of the map you are saving? One will be free to change the name, but the default would be already safe.