I thought that at first too, but even then the exception seems spurious. It would be more inline with existing Python behavior to evaluate it as undefined/indeterminate assignment order (though this would be pretty useless).
>>> a, b, c, d = {1, 2, 3, 'a'}
>>> a
'a'
Regardless, it shouldn't be surprising when writing insane code, that the language starts acting insane. Python as a whole is pretty decent when it comes to handling syntactic edge cases.
The tricky part is that the [a,b] and (a,b) in your original examples are not list/tuple literals, but a target_list according to Python's grammar [0], which can be optionally enclosed in parentheses or brackets. To be honest, I didn't know the latter were allowed, even though I've been using Python for years. IMHO, they should have just allowed parentheses. It's like the parentheses in function calls--not really a tuple, but syntactic grouping. Why have more that one way to do the same thing?
