According to a *NY Times* blog (Pogue’s Posts), Excel 2007 for Windows doesn’t cope properly when multiplying two numbers that should yield 65535 (http://pogue.blogs.nytimes.com/2007/09/27/a-big-excel-boo-boo/).
Instead, it gets 100,000.
For a very nice explanation and discussion of its relevance, see Joel Spolsky, Joel on Software blog http://joelonsoftware.com/items/2007/09/26b.html
Have a look at Joel’s blog, and pay especial attention to the talk about testing – the fact that the bug appears to be in the presentation layer, and the testing is probably going to take results from before the presentation layer kicks in.
One more thing occurs to me. If there is this sort of bug that happens on 12 out of 18446744073709551616 possible cases, and it has only just been found, how many more are out there?