Assigning a variable to the result of an untyped method removes any existing type constraints

from typing import Any, Optional

def foo() -> Optional[int]:
    return 42

raz: Any

def bar() -> int:
    x = foo()
    if isinstance(x, int):
        reveal_type(x)
        x = raz()
        reveal_type(x)
        x = x + 42
    return 0

$ python3.6 -m mypy --strict-optional test_optional_assign.py
test_optional_assign.py:11: error: Revealed type is 'builtins.int'
test_optional_assign.py:13: error: Revealed type is 'Union[builtins.int, builtins.None]'
test_optional_assign.py:14: error: Unsupported operand types for + ("Optional[int]" and "int")

I would have expected the revealed type at like 13 to be Any.