Ghouls not effected by explosions?

[Geeves83]

Has anyone else ever run into any explosion-invincible ghouls before? I've run into a few ghouls that don't react to explosions at all....don't take damage, don't receive effects (like for the incendiary grenades) UNLESS I happen to be in the blast radius, too. I've looked this up on the net, but I can't find any mention of anyone else having this problem, so i figured i'd post here. At first I thought it was a result of messing around with one of my mod esps, but then i deactivated it (along with all others) and it's still happening. Everything else I've shot that i've come across (which has only been people, bighorners, bloatflies, geckos and molerats so far) is reacting just fine.