This is an eBook sample from B&N. I've added in Charis SIL as the embedded font. The first sample and the second sample are identical except for the CSS. The CSS in the first sample is ansi encoded and the second sample has the CSS UTF-8 encoded.
When you view the first sample (using ADE), the embedded font is as it should be. When you view the second sample (using ADE), the embedded font is not correct. It's bold where it should be normal.
Why this is, I do not know. It's a very odd bug. The code in both CSS is perfectly OK.