(A - B) is not equal to A - B, apparently

So in cell A1 have the following formula:

A1 =SUM(AE10:AP10)-O10, which returns 0. O10 is yearly revenue, cells AE to AP are monthly revenues, which are calculated on the basis of $O$10/12, so it's normal that I get 0 in A1. I double-check by doing B1 = A1 = 0, which gives me TRUE.

However, when I do A1 =(SUM(AE10:AP10)-O10) [so with brackets], suddenly B1 = A1 = 0 gives me FALSE. Any idea why that might happen?

Thanks!
EG

Also asked the above question here: http://www.mrexcel.com/forum/excel-q...ml#post4439839