On September 25th, 2007, David Gainer of the Microsoft Excel group did a post acknowledging a Microsoft Excel 2007 math bug involving calculations of numbers around 65,535 and 65,536.

An example bug is: 77.1 * 850 for which Excel returned 100,000 instead of 65,535.

According to David, the issue was due to change in the Excel calculation logic in Office 2007. The bug affects Excel 2007 and Excel Services 2007.

The patch has been posted here.