Well, if one assumes the point of allowing 'human-friendly' relative dates such as 'yesterday' is to make usage more intuitive, then the 24-hour-offset is probably incorrect behavior. That would explain the quantity of bug reports you are seeing.
Perhaps the 'yesterday' directive ought to just go ahead and assume the recommended noon reference point, rather than the current moment? That would certainly reflect the general meaning of the term 'yesterday' more accurately. It seems odd to explicitly permit a natural-language term and then use a definition for it that differs from what a natural-language user probably means.
