Text message order

In the last few days something has changed with text messaging in terms of showing most recent texts. If I get a text fom Person A on Monday and a text from Person B on Tuesday, the one from person B is at the top because it's newest. If I open the person B conversation and delete the Tuesday text, it used to be that Person A would now appear at the top since that became the most recent message based on timestamp. But now person B remains at the top because they were the last person to text me and since I've deleted their most recent message, it shows whatever their last message was that I haven't deleted even if it's from a month ago. How do I fix this?