Mypy rejects valid nested class inside of a NamedTuple class definition

I think I've found a bug in NamedTuple handling:

from enum import Enum
from typing import NamedTuple

class T(NamedTuple):
  class State(Enum):
    A =1
  state:State

print(T.State.A)
print(T(state=T.State.A))

This runs fine in Python3.7 but mypy master head issues the following error:

Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"

setup.cfg:

[mypy]
python_version = 3.6
cache_dir = _build/mypy_cache
mypy_path = ~/work/pithy:./lambda
check_untyped_defs = True
disallow_subclassing_any = True
disallow_untyped_calls = True
disallow_untyped_defs = False
ignore_missing_imports = False
show_column_numbers = True
show_none_errors = True
strict_boolean = False
strict_optional = True
warn_incomplete_stub = True
warn_no_return = True
warn_redundant_casts = True
warn_return_any = True
warn_unused_configs = True
warn_unused_ignores = True

Start by running the minimal Python reproducer against mypy and trace the NamedTuple handling that emits the invalid-statement diagnostic. Confirm that a nested Enum class is accepted inside the NamedTuple definition and that the example type-checks without this error; add regression coverage where the existing NamedTuple tests are located.