I ran into this recently, I'm sure many others did too (I'm not the issue poster).

https://github.com/eventlet/eventlet/issues/702

https://github.com/benoitc/gunicorn/pull/2581

While the bug does seem pretty critical for websocket users, the patch-version-change ended up breaking any application that uses gunicorn with eventlet (even if you don't use websockets).

It feels slightly like my fault, because eventlet has been at v0.x.x for 9 years now. I used to be a bit hesitant about using anything that couldn't declare a version 1.0.0. I guess I've learned my lesson and just won't use any v0 library except in hobby projects now.

It really depends on the bug? If it is a bug that causes your program to crash or return obviously invalid output then it's probably OK to fix it. But if the 'bug' does something useful that just happens to be undocumented or contradicts the documentation, then you need to be a lot more careful about 'fixing' it. Especially if it's clear that lots of people are relying on that bug as a feature.