strange difference between list() and tuple() using iter()

[Skaperen]

when using iter() then to get the items from the iterator using list() or tuple() there is a strange difference. here is the demo:

Output:
lt2a/phil /home/phil 86> py
Python 3.6.9 (default, Oct  8 2020, 12:12:24) 
[GCC 8.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> a=['foo','bar','boo','far','baz']
>>> a
['foo', 'bar', 'boo', 'far', 'baz']
>>> list(x for x in a)
['foo', 'bar', 'boo', 'far', 'baz']
>>> tuple(x for x in a)
('foo', 'bar', 'boo', 'far', 'baz')
>>> list(iter(x for x in a))
['foo', 'bar', 'boo', 'far', 'baz']
>>> tuple(iter(x for x in a))
('foo', 'bar', 'boo', 'far', 'baz')
>>> b=iter(x for x in a)
>>> list(b)
['foo', 'bar', 'boo', 'far', 'baz']
>>> tuple(b)
()
>>> 

so, tuple() varies from list().

even more strange, the variance of tuple() depends on if the iterator was stored in a variable (b in this case). is there an explanation of why it differs like this or is this a bug? can someone try this in 3.7 or 3.8?