Odd behavior when creating namedtuple

I am writing a descriptor and attempting to annotate using the typing module. I think I have found a bug, but since I am pretty new to mypy I am posting it here. Below is the behavior I encountered:

# test_file.py
from collections import namedtuple

class Snapshot:
    def create_tuple_type(self, name: str):
        self.tuple_type = namedtuple(name, [])  # line 6

def create_tuple_type_1(name: str):
    x = namedtuple(name, [])                    # line 9

def create_tuple_type_2(name: str):
    return namedtuple(name, [])

running: mypy test_file.py prints:

snapshot\tinutest.py:6: error: NamedTuple type as an attribute is not supported
snapshot\tinutest.py:6: error: namedtuple() expects a string literal as the first argument
snapshot\tinutest.py:9: error: namedtuple() expects a string literal as the first argument
Found 3 errors in 1 file (checked 1 source file)

I am confused:

• what does the first error mean, I am not using NamedTuple (also NamedTuple is not a type, but a function)?
• I explicitly set name to be a string, why the second and third error (it says 'literal', but there is no reason this would not work, it actually does in practice ;-)?
• why does create_tuple_type_1 give an error, while create_tuple_type_2 doesn't?

This might more issues, but since they occur so close together, they might be correlated?

The reproducer is the inline test_file.py example; start by running mypy against it and comparing the diagnostics for the attribute assignment, local assignment, and return cases. Trace the handling of namedtuple calls and annotated attributes, then define done as consistent, documented behavior or corrected diagnostics for all three examples.