Trouble with fonts subset

I often embed custom fonts in my epubs and I never have a problem when running font subset in calibre.

Except for one font. Calibre removes all the fonts, saying that they are not in use.
Since calibre has no problems with other fonts I use, I think maybe the problem is with the font itself.
But I know nothing about fonts, so...

Any idea ?
Thanks.

See the test file. The fonts files were downloaded from FontSquirrel here.

Attached Files

test.epub (285.7 KB)