So, then I guess both
(curdata >> 16)
and
~(curdata & 0xFFFF)
result in unsigned ints that get compared? If they resulted in unsigned long then the first statement would evaluate as 0000nnnn and the second as FFFFnnnn, since the leading 0's would be inverted. This is obviously not the case.
Regardless, it is working right in the "fixed" version with (~curdata & 0xFFFF) which is good.