I couldn't replicate your results with that query on GPT-4.
Prompt: What’s heavier, a kilogram of steel or two kilograms of one kilogram feathers?
GPT-4: Two kilograms of one-kilogram feathers are heavier than a kilogram of steel. Despite the misconception caused by the popular question about what's heavier—a kilogram of steel or a kilogram of feathers (they are equal)—in this case, you are comparing two kilograms of feathers to one kilogram of steel. Hence, the feathers weigh more.
Prompt: What’s heavier, a kilogram of steel or two kilograms of one kilogram feathers?
GPT-4: Two kilograms of one-kilogram feathers are heavier than a kilogram of steel. Despite the misconception caused by the popular question about what's heavier—a kilogram of steel or a kilogram of feathers (they are equal)—in this case, you are comparing two kilograms of feathers to one kilogram of steel. Hence, the feathers weigh more.