This is a known AO3 bug for prompt meme-style AO3 challenges. It's been a bug since 2015 if not earlier, and I have no idea when AO3 will fix it. (They definitely know about it.) Sadly, it's not something I have any control over on my end. All I can really recommend is that people who are worried about it may want to wait to claim a prompt until right before posting their remix.

It didn't really occur to me that this would be something people would worry about. I think the ship has more or less sailed for this year's round, but next year I'll make sure I mention it somewhere for the Madness round.