i don't have windings and i can't test.
but i suppose that windings does not have a "n" and that's why you get a square.
scribus shows invalid characters with a red outline and print them as spaces.
other programs print them as rectangles.
... and yes, we had already had a user complaining that she wasn't getting her checkboxes in the pdf...
... and, yes, probably, windings does have checkboxes. but it's not those rectangles : - )