So I've submitted a bug report against integer for this - in case there's someone who cares enough to fix it.

Turns out that the integer pragma only works with integer values in the range -(2**63) .. (2**63-1).
On 32-bit perls that range becomes -(2**31) .. (2**31-1).
Yes - it's that crappy, and I doubt that anyone cares.

It's all there in the integer docs if one reads that documentation properly - which I didn't do.

Wiping egg off face (... yet again),
Rob