Chain of spurious type warnings after clearing PyCharm cache

I'm noticing spurious type warnings popping up a lot after the cache is refreshed. It seems to be connected to not having a `-> None` return type annotation on `__init__` methods that use Python 3.6 type hints on `self` variables, which I thought was not required. It can cause a chain of warnings when different types depend on each other.

Just wondering if anyone else has been running into this. 

https://youtrack.jetbrains.com/issue/PY-25471

https://bitbucket.org/planders/type-hint-problem