This is a by now well known bug in Excel 2007.
I'm guessing what happened here is that there's an off-by-1 error in a comparison somewhere (i.e. ">= 65535" instead of "> 65535"), and the 32-bit quotient/remainder print routine kicks in. Since the number is already smaller than 100000, it probably hits a fall-thru case where the quotient is assumed to be 1, and there's no remainder, hence it is printing 100000.