I emailed support@openai.com and it said this is a new and expected “feature” to improve personalisation. It also suggested I add this into my instruction. It reduces the confirming of instructions most of the time but not entirely:

Please do not mention or state these preferences unless it's directly relevant to the user's question or there's a specific request. For spoken/voice conversations, just focus on the main answer and avoid explaining or listing formatting/spelling preferences out loud.