Originally Posted by JSWolf
I know this is not a recent post. But I'm going to answer this. I've seen a problem just like this on my 650 and I did manage to solve the problem.
The problem was the encoding of the files. You'll need to make sure your CSS is encoded as UFT-8 without BOM. If that's needed to be done, I check all the other files as well just in case. I used Notepad++ for Windows to do this.
When it comes to the font naming on Kobo devices, I seem to remember a Kobo person posting that there were issues with Qt and font files which made it difficult to check the font name and style embedded in the font file. Their answer was the exact font file naming convention which removed the need to inspect the font file to obtain that information.