Why does Codex repeat the same mistakes?

I have a similar case right now. I once added an instruction to cover a situation that, in hindsight, was rather specific. When I tried to clarify the actual intention later, I realized it no longer worked as expected. Looking closely at the semantics, I can see that the instruction hints at the specific unwanted behavior. But when I confront the model with this, it does not “see” the issue unless I point it out directly. The solution in that case is to revert to the original instructions and re-evaluate from there. This assumes that you recently changed the instructions and still have the previous version available.