I tried to replicate the PR's Windows failures. I really did. But I barely got anything working when I tried. If anyone out there knows about running tox on Windows and wants to help me out with this, then please take a look at my PR.
For now, I'm going to stop thinking about this, because it just makes me confused and angry.
In happier news, I finished the puzzle hunt earlier today. I'm going to finish this entry, because it's actually bothering me to look at my own account of trying to replicate the failures.
EDIT: The problem with my tests was obvious in retrospect, given my Windows knowledge, and is now fixed. Now to act on the various bits of feedback, in a few hours.