I recall reading somewhere on Joel on Software that I can't find at the moment that Microsoft did this deliberately to duplicate a bug in Lotus 1-2-3, because t

I recall reading somewhere on Joel on Software that I can't find at the moment that Microsoft did this deliberately to duplicate a bug in Lotus 1-2-3, because they needed perfect compatibility with formulas and dates with 1-2-3 to get people to switch over. And Lotus 1-2-3 reportedly had this bug because, at the time it was written, the code to account for that case correctly legitimately took up too much space and was dropped, with Lotus figuring that not too many people would notice. And of course, Microsoft can't change it now, or else they'll potentially break a ton of people's spreadsheets that already work around it.