If I am making a thread with the inline editor (the editor when you can still view threads in a forum, and not the page dedicated to a new post), and click "Accept cookies" on the prompt at the bottom, it'll reload the page and delete the contents of my post in progress.
Sometimes I reply without checking what page I'm on (usually when coming from what's new) and I usually want to reply only after reading to the latest page. Maybe displaying a small "you're not on the latest page" notice might be helpful. I'm aware a notice does pop up after you finish your...