I just read something yesterday about how if you have a witness proxy then your voting on steem proposals is moot if your witness proxy does not also vote on it! I haven't voted on proposals yet, I still need to figure that function out - but that seems like an overreach of authority to me, so I hope everyone stops using witness proxies. It isn't super hard once you've found some that you feel OK about supporting to just check in every now and then and make sure they're still active; any wild news (like in your case where you wanted to support those against HF21) will probably pop up in your feed and alert you anyway as Steem loves nothing more than talking about Steem, lol, so it would be unusual if they did something egregious, to not hear about it.