Yes, the identifiers you've mentioned aren't in the helpfile for a reason, but there is no reason for $nickmode not to be in there. It's not a bug per se, but this is the closest relevant forum for what he's posting.
Unreal IRCD and like IRCD's have modes qaohv o can't kick a and a cant kick q. the respective prefixes are ~&@%+ but alot of servers remove the ~& prefixes but qa still exist and have the same effect. if you are op and don't want to try and kick qa because you can't and modes ~& are removed it wont work. So using $nickmode is much more advantages to use when making such scripts. Wish I knew it existed sooner..
$leftwincid isn't documented either. Its function is pretty obvious if you know what $leftwin is (which is documented). Just thought I'd share this newly found identifier (as far as I know, it hasn't been mentioned in the past).