Smarten quotation marks conversion

I've come across a Mobipocket ebook converted using calibre 0.7.1 that used U+0093 (Set Transmit State, UTF8 encoding C293) and U+0094 (Cancel Character, UTF8 encoding C293) for left and right double quotation marks.

These are not the right characters to use - they should be U+201C (Left Double Quotation Mark, UTF8 encoding E2809C) and U+201D (Right Double Quotation Mark, UTF8 encoding E2809D).

Does/did calibre smarten quotes with the wrong characters? Or was this a source text problem?

I could delve deeply into this and find the answer myself, but I'm hoping that someone here has the answer at their fingertips (and that the answer is that it's a source text problem!).

Thanks.