That's a really common thing. In Polish copyright law, any license expires after five years by default unless it explicitly states that it's perpetual - which d

That's a really common thing. In Polish copyright law, any license expires after five years by default unless it explicitly states that it's perpetual - which doesn't mean it becomes irrevocable at all (in fact, it's easier to revoke a perpetual license than a timed one). That said, this is an open license rather than a regular two-sided contract, which makes a lot of things about it untested in courts and there are some pretty good legal arguments for considering it irrevocable flying around (just like in case of GPLv2, for example).