It hasn't failed yet when run "straight".

Here's the issue, though. I'm going to be introducing Python as the scripting language of choice, to a bunch of people who are less than fluent in programming. Because debugging is not an obvious concept to them, they are going to hunt for problems by sticking in print statements everywhere, and the environment is inherently multithreaded, so it's hard for me to imagine they won't experience this bug. I hit it in my very first multithreaded experiment. And I can't possibly ask them not to use IDLE - without syntax coloring and a friendly editor to show them which line is wrong, they will never get off the ground.

It would be tolerable if there was at least a traceback, but if threads vanish silently, they will not realize it's a environment problem; they will either assume that they did something inexplicably wrong and that "scripting is too hard", or it will get around that I provided a "broken" solution.

So even if it's "just the IDE", it's still life and death for this project. "Won't fix" probably means I have to abandon Python.