Sep 25, 2007 Excel 2007 Multiplication Bug
Several researchers have reported a serious multiplication bug in Excel 2007, which has been reported to Microsoft. The example that first came to light is '=850*77.1' — which gives a result of 100,000 instead of the correct 65,535. It seems that any formula that should evaluate to 65,535 will act strangely.
Suppose the formula is in A1. =A1+1 returns 100,001, which appears to show the formula is in fact 100,000... =A1*2 returns 131,070, as if A1 had 65,535 (which it should have been). =A1*1 keeps it at 100,000. =A1-1 returns 65,534. =A1/1 is still 100,000. =A1/2 returns 32767.5."