Unexpected error when inheriting a class from Popen and overriding some method in it

[actionless]

• Are you reporting a bug, or opening a feature request?
  Bug

• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

import subprocess
from typing import List, Tuple


class MyPopen(subprocess.Popen):

    def communicate(self, _input=None, _timeout=None) -> Tuple[bytes, bytes]:
        return super().communicate(_input, _timeout)

def interactive_spawn(cmd: List[str], **kwargs) -> MyPopen:
    process = MyPopen(cmd, **kwargs)
    process.communicate()
    return process

• What is the actual behavior/output?

$ mypy mypy_subprocess.py
mypy_subprocess.py:13: error: Incompatible return value type (got "Popen[Any]", expected "MyPopen")
Found 1 error in 1 file (checked 1 source file)

• What is the behavior/output you expect?

$ mypy mypy_subprocess.py
Success: no issues found in 1 source file

• What are the versions of mypy and Python you are using?
  Do you see the same issue after installing mypy from Git master?

$ mypy --version
mypy 0.730

(env) $ mypy --version
mypy 0.740+dev.583b99e5096c979043a63dcf92bf3f0d5993d03a

NOTE: it's not reproducing with 0.720

$ python --version
Python 3.7.4

• What are the mypy flags you are using? (For example --strict-optional)

• If mypy crashed with a traceback, please paste
  the full traceback below.

[msullivan]

Yeah this got introduced in 0.730. I need to spend some time tweaking the rules for __new__ return types maybe.