Thanks to John Bartow for sending a link to Excel Can't Multiply. I tried it, and it's true. Be sure to read the first response because he share some interesting insight.
I can't add anything to the article. I found that adding 1 to the result, =850*77.1 +1, returns 100,001. However, adding a value via a dependent reference, =cell + 1 forced the right answer, at least with the few I tried. Also, adding a value other than 1 forced the right answer in the full expression: =850*77.1 + 2
I didn't play anymore with it much. I was curious how deep the error might ripple through dependent expressions.