Just for reference: I've just spent quite some time debugging missing coverage with pytest, and it turned out that part of it is because of this issue.  Most of the pdb related tests run in a subprocess (via pexpect), but not all of them.

I am using a wrapper now to restore this manually (https://github.com/pytest-dev/pytest/pull/5406).

Even though I was aware of this issue, it took me quite a while, mainly because this started out with slash related issues for Windows only, and I was debugging this on/via CI only at first.