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!

Start with the provided isinstance reproducer and compare mypy's handling of tuple, Tuple[Any, ...], and plain Tuple. Trace the type-checking entry point for isinstance calls and determine the intended behavior from the linked Python documentation. Done means the three equivalent forms receive consistent, documented diagnostics, with tests covering the reproducer.