@dpierron: calibre does not aim to preserve your CSS class definitions, instead it tries to simplify them as much as possible to improve rendering speed on the device, which is why font-family was moved. As long as the correct *content* still has the font-family rule, it's not a bug.
As for font-face, yeah that's a bug, but it will probably only be fixed when I add support for font embedding to calibre, until then font-face is rather meaningless.
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