I've seen this with troll and ogre guards. If you root them, they don't respond as they should. For example, they won't turn to face the attacker. You can root them from the side or behind and there's no reaction.
If they're casters and have a casting script, they WILL turn toward the attacker. But the warrior types, who don't do anything if the attacker isn't in melee range, don't react at all. They WILL engage in melee if you get into melee range.
May be with other guards too, these are the only ones I've been killing lately.
Not a big deal at all, but a bug's a bug.
[You must be logged in to view images. Log in or Register.]