Comment 5 for bug 1736973

FWIW I'm not able to reproduce this issue (Windows 10 x64). If I delete a font from "C:\Windows\Fonts" it's typically gone. Only exception were some font's with non-ASCII characters in file name I experimented with some time ago.

One thing that can be tried (if it's the issue Tyler describes it won't help, though) is to delete the font cache which can be found in the folder
  %localappdata%\fontconfig\cache
which will force Inkscape to re-create it (in case it got corrupted for some reason or could not be updated)

If that does not help there's not much we can do, though, and it should either be carried upstream to fontconfig devs or (as they probably should not be bothered with Microsoft quirks either) to Microsoft themselves...