You enter hex numbers in the format "0xnnn". I tried to duplicate your result and I'm seeing the same strange thing. If I just put in the constant 0x80000000 and do nothing, just wire out the value, I get 0 out. If however, I define x = 7fffffff and then add 1 to it, I get 80000000 out. If I use decimal 2147483648, it works. If I define the variable as an int32 and 0x80000000, it works as expected. I don't use the formula node that much but it seems like a bug to me. You might want to report this one to NI.