Trouble using alternate font styles

I’m having trouble loading alternate font styles into a SpriteFont asset. I’m trying to use Open Sans, which works fine for the default font style, but also has a set of other font styles (taken from a set of TTF files comprising the Open Sans font as a whole). Here they are in Photoshop:

Here it is as a group in my Windows Fonts folder:

And here they are, copied to regular file system entries:

The problem is, when I try to select anything other than Open Sans Regular, the asset fails to render a thumbnail or preview correctly, and also doesn’t appear to compile, as when I try to load it in-game, I get an InvalidOperationException complaining that the asset doesn’t exist. Here’s what Paradox Studio looks like with Open Sans Regular and Opens Sans Semibold both loaded:

Any help/advice would be appreciated, as I’d really like to use the variant font weighting.

Edit: Added an issue to Github: https://github.com/SiliconStudio/paradox/issues/147