I’m having similar issues. Even specifying a length is completely ignored. I can say “answer in 100 words” or “4 sentences” or “2 paragraphs”, and GPT3 acts like that specification isn’t even there.
Longer, more specific prompts that require it to provide more information are fairly effective, but I often still have to regenerate the answer 2-3 times before it gives one that will work. Unless someone has some information otherwise, I would consider this a bug - the system consistently ignores an instruction that it’s given.