Generally I use my Ignore list as a temporary time out, rather than a permanent ban. When I can't remember why I put a person on ignore any more, I take them off. I'm trying to flush the list clear right now, and it only let me remove two of the four names, and those only after multiple attempts. The two that are left keep saying "You can't ignore that person". This happens if I try to unignore from their user profile or one of their posts as well.