I also try to avoid negative instructions. No scientific proof, just a feeling the same as you, "do not delete the tmp file" can lead too often to deleting the tmp file.
It seems that that problem hasn't really been "fixed", it's just been paved over. But I guess that's the ugly truth most people tend to forget/deny about LLMs: you can't "fix" them because there's not a line of code you can point to that causes a "bug", you can only retrain them and hope the problem goes away. In LLMs, every bug is a "heisenbug" (or should that be "murphybug", as in Murphy's Law?).
"Don't think of a green elephant"
Alan Watts talked of this concept where the harder you try to suppress a thought or sensation, the more mental energy you give it, making it stronger.