Automatically scale grid

What does the 'Automatically scale grid' option do?
I don't notice any difference with it disabled.

switching Automatic scale grid on & off, I discovered the Print-Preview screen is affected
to the point 80% of the drawing lines disappear !

coming back to the Application Preferences panel I witnessed that simply opening and closing it
triggers the bug which almost erases the preview screen...
note that the bug only performs if and only if Print-preview is active
when closing the panel.  You must close and reactivate Print-preview to see all the lines :)

I did some investigating and found that disabling this option requires changing
X Spacing / Y Spacing
from 'auto'
in Current Drawing Preferences -> Grid.