Type inference in high level function

For fully valid code got:
error: Argument 1 to "map" has incompatible type overloaded function; expected "Callable[[Iterator[_T], int, None], Iterator[_T]].

In foo.py:

from typing import Generic, Iterable, Iterator, Sequence, TypeVar
_T = TypeVar('_T')

class Windowed(Generic[_T]):
    def __init__(self, it: Iterable[_T], size: int) -> None:
        self.it = it
        self.size = size

    def __iter__(self) -> Iterator[Sequence[_T]]:
        iters = tee(self.it, self.size)
        slices = map(islice, iters, count(0), repeat(None))
        return zip(*slices)

However islice has overload:

def islice(iterable: Iterable[_T], start: Optional[int], stop: Optional[int],
           step: Optional[int] = ...) -> Iterator[_T]: ...

Using mypy 0.750 from PyPI, on python 3.7.5. Running it via mypy foo.py

Reproduce the diagnostic from foo.py with mypy 0.750 on Python 3.7.5, focusing on the map(islice, iters, count(0), repeat(None)) call and the islice overload shown in the issue. Trace the type inference for the overloaded function and verify that the valid example no longer reports an incompatible argument error.