Yeah, bit 12 in the EXTH flags seems to be the sole trigger
.
So here's an updated patch that doesn't inject a fake fontsignature anymore, and with a crappy hackish conditional that *should* set the correct bit in the bitflag only when we actually *have* embedded fonts. I *think* I patched joint KF8 output too, but I've only checked standalone KF8 files. (And I only patched the mobi7 header, not both, unlike Kindlegen, since I don't see how it would be useful on a mobi6...)
EDIT: Updated patch with a completely unrelated fix, but it's in the same file, and I don't feel like setting up quilt right now... Anyway, the 'rights' metadata entry was injected twice in the exth headers.
EDITē: Killed deprecated attachments. Fix merged upstream.