so.cl is a short enough domain that some browsers might forbid it from setting cookies, since it's the same length as .co.uk (and letting sites set cookies for the whole .co.uk space would be a massive privacy violation).
Each browser has their own way of handling this - public suffix is Mozilla's solution but I don't know if any if the other browsers are using it directly (I'd be surprised if IE didn't have their own approach).
While I see the point (and some TLD do have A records), I've never had issues setting cookies from two letter second level domains. At least with modem browsers that doesn't seem to be an issue.
