I’m making a fallback font to show the unicode codepoint of characters which can not be displayed by any other fonts, something like Unicode BMP Fallback SIL (Unicode BMP Fallback Font). But I find that on Windows, a font is said invalid and can not be installed if it contains both uniFFFE and uniFFFF. If it only contains one of them, or neither, it is ok. How many other characters are there in this font does not matter. This problem does not exist on macOS. Is it a problem of Windows? or a problem in Glyphs exporting?