hmmm, good question....
don't know, maybe there's a difference when storing the value in a field and when store it in a variable?
The docs says that for bittest() / bitset() the second parameters should be from 0 to 31, but BitSet(0, 31) = -2,147,483,648 wich is out of the VFP integer limits....

>So Why would this work fine ?
>

>n=BitSet(0, 31)
>? n
>? Bittest(n, 31)
>

>
>>Becareful because all the bitwise() operation works only on integers, so from -2,147,483,647 to 2,147,483,647, no support out that range, it's a VFP limitation....