It absolutely would - if you accidentally pressed back or refreshed the page, if fields don't pass validation, if there's a server error or a network issue when you try to submit, if your credentials expire while you're editing, etc.
Not defending meetup but people have every reason to try to override default UA behavior.
What we get is what you described.
I wish more editing forms were just a <form method="POST"> with <input value="whatever" /> and an <input type="submit"> for me to click.
No system designed around that would ever eat up half our edits.