Microsoft has confirmed the existence of a serious bug in Excel 2007 that can cause an incorrect amount to appear in a cell. The problem that has been isolated so far occurs when a calculation should produce the result of 65535. Instead of the correct result, Excel displays 100000. For example, enter the following formula in an Excel 2007 cell:
You will see that 100000 appears as the result. Other formulas have the same effect.
It should be noted that, although the spreadsheet displays 100000, the value of the cell is correct at 65535. So if you use the cell in another formula (for example, if the mistakenly displayed presentation of 100000 appears in cell A1 and you enter the formula =A1*2 in another cell, you will see the correct result of 131070.
The problem is manifesting itself in many, but not all, calculations that should produce a result of 65535. For example, the formula =13107*5 produces the correct result of 65535.
According to a description that appears on the Microsoft Developer Network Excel team blog, this is where the problem lies:
"So what, specifically, are the values that cause this display problem? Of the 9.214*10^18 different floating point numbers (floating point on wikipedia) that Excel 2007 can store, there are 6 floating point numbers (using binary representation) between 65534.99999999995 and 65535, and 6 between 65535.99999999995 and 65536 that cause this problem. You can't actually enter these numbers into Excel directly (since Excel will round to 15 digits on entry), but any calculation returning one of those results will display this issue if the results of the calculation are displayed in a cell. All other calculation results are not affected."
Programmers at Microsoft are aware of the problem and are working on a fix. No date for a correcting update has been projected yet.