Suppose I have a.py:
import b # type: ignore
b.foo()
and there's no b.py or b.pyi on the path. This checks without errors, and in incremental mode does not record b as a dependency of a.
Now I create a valid b.py, and re-run mypy -i a.py (this is with a warm cache). I had expected it would mark a as stale and re-parse it, but it doesn't.
A suspicious change is 4889c0c ("Warn about unused '# type: ignore' comments (#1695)") which apparently made the effect of # type: ignore on imports much more severe, also without -i.
(This seems related to #1904 but I think it's a separate issue. Also, I think it's low priority since it only applies to ignored top-level imports, not to imports of submodules of packages.)