Maybe it's possible that some entity within that country could pick up the code, slap their own copyright on it, and claim to now own the code? Probably a long stretch but maybe that's the case.
I'm not a lawyer, but as I understand it, the issue is not 'countries that don't recognise the public domain', but rather 'countries that do not allow authors to donate their works to the public domain', which includes the USA (since 1978):
