isinstance(x, Tuple) fails when equivalent expressions don't

reproducer

from typing import Any, Dict, Tuple

x = (1,2)
isinstance(x, tuple)
isinstance(x, Tuple[Any, ...])
isinstance(x, Tuple)

observed behavior

$ pipenv run mypy test.py 
test.py:6: error: Argument 2 to "isinstance" has incompatible type "_SpecialForm"; expected "Union[type, Tuple[Union[type, Tuple[Any, ...]], ...]]"

expected behavior
The python documentation states

A plain Tuple is equivalent to Tuple[Any, ...], and in turn to tuple.

If the above is true, IMO either all of the examples should raise errors, or none of them should. Only the third example is raising an error right now. I'm not quite sure what the error means in any case.

environment
master as of 2019-04-15

$ pipenv graph
mypy==0.710+dev.2c8a809693cf5be0b29d272d7f0711521bd4a55a
  - mypy-extensions [required: >=0.4.0,<0.5.0, installed: 0.4.1]
  - typed-ast [required: >=1.3.1,<1.4.0, installed: 1.3.1]

As always, thanks for all the work you do here!

Beginne mit dem bereitgestellten isinstance-Reproduzierer und vergleiche, wie mypy tuple, Tuple[Any, ...] und einfaches Tuple behandelt. Verfolge den Einstiegspunkt der Typprüfung für isinstance-Aufrufe und bestimme das beabsichtigte Verhalten anhand der verlinkten Python-Dokumentation. Erledigt ist die Aufgabe, wenn die drei äquivalenten Formen konsistente, dokumentierte Diagnosen erhalten und Tests den Reproduzierer abdecken.