If an event never starts (for whatever reason, on this case the organizer lost the sign up sheet) it stays on the list indefinitely and cannot be removed. Couples with the lack of dates for on demand events, it's confusing.
I saw in a previous response that they will auto remove after 28 days, but that's a month, or 4 FNM events (for example) where you'll have a zombie event cluttering your app.