[Toxaris]

I found the issue with the ePUB. The program is 'correct'. The 'King-things' font file is only used as bold. However, in the font-face it is not specified that the font is bold. If it is not specified, it will take the default, which is normal for both font-weight and font-style.
It has to do this, because a font-family can have multiple members and the used glyphs can change per member. For the defined member here, there are no glyphs in use.

If you would add 'font-weight: bold;' in your font-face declaration it will work as it should.

I hope I made it clear...