Yeah, I'd guess the TT hinting instructions (if any) are a bit weird, which isn't surprising on a font as old as this one, with multiple formats/hinting instructions for each format piling up long after the font has been designed, and the settings used by the mobi reader engine don't play nice with that (in fact, the mobi reader doesn't use bytecode TT hinting instructions, at least in fw 2.x, AFAICT).
It should theoretically be possible to tweak the font to play nice with the Kindle's settings, but since the font is copyrighted, and I don't own Microsoft Office, err...
And PDF embeds usually prefers the Type1/2 (Postscript) (all of them more or less being Adobe's babies) variants of a font over TrueType (more or less *not* Adobe's baby
[Apple's, in fact]), which may explain why you're seeing a different rendering with a PDF, because they're using a whole different set of hinting instructions, and outline tracing method (quadratic bezier curves vs. cubic bezier curves).