I agree, some aren't displaying correctly.
I just did a test - have created a font myself and attempting to test it out in various places, so far Word and Inkscape just now. Basically it's one font that I saved 7 various ways, taller, shorter, etc, but basically the same, so there were 7 file names. However, I had deleted 6 of them, so I can't figure out why Inkscape sill has 7 showing (can't figure how to delete them either, never had this problem). Only one, the last one installed, showed up with my actual font previewed, the others showed as whatever default Inkscape uses. Even stranger, when I went to c:\Windows\font, only the last one shows as being installed. I even checked, and no fonts are hidden. So not sure what is happening.
I would suggest that you also go to c:\windows\fonts, and click on the font preview, just for comparisons sake.